1. (a) T (b) T (c) T (d) F (e) T

By contrast to the situation in normal ongoing pregnancies, in cases of miscarriage, onset of the maternal intraplacental circulation is both precocious and disorganised. Thus it starts at an earlier stage, and occurs randomly throughout the placenta. This is most likely accounted for by the fact that in 70% of these cases extravillous trophoblast invasion is superficial, and consequently plugging of the spiral arteries is less complete. In normal pregnancies, villi sampled from the peripheral region of the placenta demonstrate elevated levels of the chaperone protein HSP70, nitrotyrosine residues indicative of peroxynitrite formation, and morphological evidence of degenerative changes within the syncytiotrophoblast compared to those from the central region. By contrast, in miscarriages, the levels of HSP70 and nitrotyrosine are increased in villi sampled from the central region of these placentas as well as in the periphery. There is also an increase in the apoptotic index compared to control placentas of a similar gestational age, and morphological evidence of degenerate syncytiotrophoblast sloughing off in some areas. During the first trimester, the syncytiotrophoblastic layer of the villous tissue contains low concentrations of the principal antioxidant enzymatic defences, copper/zinc superoxide dismutase and catalase. Consequently, the trophoblast at that stage is much more sensitive to oxidative stress than later during pregnancy. The efficacy of the antioxidant defences provides the other half of the pro-oxidant-antioxidant balance that determines the oxidative status of a tissue. Thus polymorphisms in the enzymes detoxifying ROS have been linked to an increased risk of miscarriage. Equally, there is some evidence that selenium deficiency, which will reduce the efficacy of glutathione peroxidase, is associated with miscarriage.

2. (a) T (b) F (c) F (d) F (e) F

There is now irrefutable evidence of placental oxidative stress in cases of early-onset pre-eclampsia, including increased concentrations of protein carbonyls, lipid peroxides, nitrotyrosine residues and DNA oxidation. The cause for the oxidative stress is thought to be vascular, for early-onset pre-eclampsia is associated with deficient conversion of the spiral arteries. Exposure of placental explants to changes in oxygenation causes generation of ROS within the trophoblast and endothelial cells, as demonstrated by fluorescent markers and the formation of nitrotyrosine residues in a pattern that matches closely that seen in pre-eclamptic placentas. Furthermore, labour, in which the placenta is exposed to repeated episodes of ischaemia-reperfusion, induces high levels of oxidative stress. However, RCTs using high doses of antioxidant vit C and E from an early stage in pregnancy have shown no impact on the maternal risks of developing pre-eclampsia later in pregnancy. In these clinical trials the antioxidants were only given once pregnancy is established, by which time the feed forward cycles may already be established. It is notable that multivitamin usage during the peri-conceptional period is associated with a reduced risk of pre-eclampsia among lean or normal weight women. Conversely, women with a low dietary intake of vitamin C have been reported to have a trend towards increased risk. The majority of cases that have no genetic or infectious aetiology are thought to arise from compromise of the maternal circulation to the placenta. This conclusion is based on the common association with high resistance uterine arterial waveforms, but also on earlier morphological studies of the spiral arteries. These demonstrated deficient physiological conversion of the arteries as in pre-eclampsia, but to a lesser degree. PROM is a condition associated with proteolytic degradation of the collagen fibres in the chorio-amnion. In this condition increase in the generation of ROS may arise from infection and inflammation, cigarette smoking, vaginal bleeding and the release of free iron, and cocaine abuse which leads to ischaemia-reperfusion. There is also evidence that deficient conversion of the spiral arteries predisposes to this condition.

3. (a) F (b) T (c) T (d) F (e) F

Hydrogen peroxide is not a free radical as it does not possess an unpaired electron. It is however an intermediate in the production and detoxification of oxygen free radicals, and so comes under the broader title of a reactive oxygen species (ROS). Having an incomplete electron shell confers the high reactivity of free radicals, such as the superoxide and hydroxyl ions. The reactivity of these radicals is such that they have an extremely short half life, and they generally react with any biomolecule in their immediate vicinity in a diffusion limited fashion. Both hypoxia and hyperoxia are linked with increased production of free radicals in mitochondria through leakage of electrons from the enzymes of the electron transport chain. In hyperoxia mitochondrial activity is increased and so more electrons are passing along the chain. As a result leakage is increased. In hypoxia there is a reduced amount of oxygen to accept the electrons at the end of the chain. Under normal conditions electrons and hydrogen ions are combined with oxygen at complex IV to form water. In the absence of oxygen electrons build up on the chain, and consequently leakage is increased on to whatever oxygen is present. This is particularly the case when oxygen is re-introduced after a period of hypoxia, the reperfusion phase of ischaemia-reperfusion. Consequently, oxidative stress can be induced under both extremes of oxygenation. Free iron ions catalyse the formation of hydroxyl ions from superoxide and hydrogen peroxide via the Fenton reaction. Hydroxyl ions are particularly dangerous due to their high reactivity. Consequently, iron is usually tightly bound to carrier proteins such as transferrin, and any iron-binding agent tends to have antioxidant properties. Free radicals cause protein mis-folding predominantly by removing hydrogen ions from thiol groups, resulting in the formation of abnormal disulphide bonds. This can cause disruption of the normal tertiary structure, leading to loss of function and protein aggregation. Attempts are made by chaperone proteins to re-fold misfolded proteins, but if these fail the proteins are ubiquitinated and broken down.

4. (a) T (b) F (c) F (d) T (e) F

In most primates, including the baboon, the trophoblast penetrates the uterine epithelium and invades the decidualized endometrium but the blastocyst remains in the uterine cavity. No capsular decidua is formed. This is in contrast with the human and great apes where the entire blastocyst is pulled into the uterine wall and becomes covered by a decidua capsularis. The description fits a New World monkey such as the marmoset but in Old World monkeys such as baboons a true intervillous space appears by the second trimester. Baboon and human are similar in this respect. Trophoblast migrates along the spiral arteries against the direction of blood flow and enters the arterial walls which undergo extensive remodelling and widening. In humans and great apes trophoblast invades by a second route from the anchoring villi at the basal plate reaching the spiral arteries from the abluminal side. This does not happen in the baboon where the extravillous trophoblasts of the basal plate (the cytotrophoblastic shell) remain sedentary. Trophoblast invasion is restricted to the decidual segments of the spiral arteries. This is in contrast to human and great apes where it is found in the inner third of the myometrium both within vessels and interspersed with the myometrial smooth muscle cells.

5. (a) F (b) T (c) T (d) T (e) F

In normal human pregnancy the placental bed is invaded by interstitial and endovascular trophoblast in both decidua and inner myometrium. Notably the endovascular invasion of the maternal spiral arteries has important consequences for uteroplacental blood supply, since this invasion is associated with a substantial vascular remodelling with elimination of the vascular smooth muscle and elastic lamina. Following reports on restricted invasion in baboons and rhesus macaques, it was assumed that the human was unique in showing deep invasion, but recently a similar deep invasion was found in chimpanzee and gorilla placental bed specimens recovered from museum collections. Pre-eclampsia is a complex disease related to disturbed maternal-fetal interaction. Impaired deep invasion is indeed a possible causal factor, but not necessarily the only or the primary one. Although data on pregnant non-human primates living in the wild are virtually impossible to obtain, there are indeed a few case reports of the occurrence of pre-eclampsia/eclampsia in the chimpanzee and gorilla, which were kept in zoos. Unfortunately no placental bed biopsies had been collected, which might have confirmed defective deep invasion.

6. (a) F (b) F (c) T (d) F (e) T

Spiral artery remodelling is a multistep process, consisting of an early decidua-associated remodelling and a subsequent trophoblast-associated remodelling step. During the early decidua-associated remodelling, the endothelium undergoes swelling, vacuolization, or both, whereas the vascular smooth muscle shows disorganization and swelling of individual muscle cells. This early remodelling step is followed by the endovascular (intraluminal) invasion by trophoblasts, which will subsequently invade the vessel wall. During the intraluminal phase of endovascular invasion part of the endothelium may be replaced by the trophoblast, but later in pregnancy endothelial repair occurs, covering the intramurally embedded trophoblast. Because of the removal of the musculo-elastic wall of the spiral arteries, these vessels no longer show any vasoactive activity (i.e. they are no longer able to contract or dilate), whereas the absence of the elastic lamina prevents rebounding of the vessel to its original diameter at the end of a muscular contraction.

7. (a) F (b) T (c) T (d) F (e) T

The primitive syncytium, which constitutes the wall of the implanted blastocyst, may release isolated syncytial cells. These may move as ‘streamers’ into the underlying placental bed. Most of the interstitial trophoblasts, however, are derived from extravillous mononuclear cytotrophoblast, which proliferate at the tips of anchoring villi and temporarily form the cytotrophoblastic shell in early pregnancy. The onset of interstitial mononuclear trophoblast invasion corresponds with the breakdown of the cytotrophoblastic shell. Mononuclear invading cells subsequently form aggregates, which may finally fuse to multinuclear giant cells. Although such perivascular clustering definitely occurs in the decidual segments of the spiral arteries, interstitial cells become more widely spread in the inner myometrial compartment. Because of their diminished likelihood to be clustered around myometrial arterial segments, a transmural migration at this tissue level only rarely occurs. On the other hand, a histological continuity has been established of intraluminal cells in serial sections of myometrial and decidual spiral arteries with the cytotrophoblastic shell. A correlation has indeed been found between the early decidua-associated vascular remodelling and the presence of interstitial trophoblast, which implies that the latter may have a damaging effect on the cellular coherence of the spiral artery wall. This effect is probably caused by the secretion of extracellular matrix-degrading enzymes by the invading interstitial trophoblasts.

8. (a) T (b) F (c) T (d) T (e) T

During the first trimester, only the decidual segments of the spiral arteries are invaded and remodelled. At the same period, the myometrial segments of the spiral arteries show decidua-associated remodelling, but the endovascular invasion of these deeper segments only begins after 14 weeks. The deep endovascular invasion occurs at mid-pregnancy and is associated with trophoblast-associated remodelling (i.e. replacement of the vascular smooth muscle and elastic lamina by invaded trophoblast embedded into a fibrinoid extracellular matrix). At 18 weeks, one-third of these vessels are invaded, and more lateral arteries are progressively invaded in the course of the second trimester. At that time, the maternal blood supply to the placenta reaches its full capacity. During the third trimester, other changes may occur in the spiral arteries (e.g. re-endothelialization and focal appearance of intimal cushions in some of the spiral arteries). There is no evidence that the latter changes play a major role in utero-placental flow.

9. (a) T (b) F (c) T (d) F (e) F

Immune cells infiltrate post-ovulatory endometrium and their number increases in the presence of fertilization. In the first trimester, 30% of stromal cells are leucocytes; 75% of these leucocytes are uterine natural killer cells. Migration of leucocytes is thought to be regulated directly and indirectly by hormones. In addition, a specific trophoblasts-derived cytokine and chemokine subset is thought to play a role in recruiting uterine natural killer cells and macrophages to implantation sites. Increased vascular permeability results from induction of vascular endothelial growth factor and placental growth factor. Veins and arteries are remodelled during early pregnancy. Venous remodelling results in dilatation and intravenous fibrin depositions in association with trophoblasts. Spiral arteries span the inner myometrium, endometrium and decidua. These arteries are high-resistance vessels and have a single layer of endothelial cells surrounded by vascular smooth-muscle cells. These spiral arteries are transformed into a low resistance vascular network by dilatation, disorganization of the vascular smooth muscle cells, fibrin replacement and endothelial replacement by extravillous trophoblasts. The uterine natural killer cells and macrophages within remodelling vessels seem to prime the decidual vessels for extravillous trophoblast invasion, which plays a role in recruiting extravillous trophoblasts to reline the vessel wall. The invasion of endovascular trophoblasts results in apoptotic death of maternal endothelial cells and vascular smooth muscle cells. This is followed by further arterial dilatation and plugging of spiral arteries. The first trimester is characterized mainly by vasculogenesis and branching angiogenesis, whereas the third trimester is predominantly characterized by non-branching angiogenesis.

10. (a) T (b) F (c) F (d) F (e) T

Invasion of endovascular trophoblasts results in apoptotic death of maternal endothelial cells and vascular smooth muscle cells. Differences in vascularization pattern include: enhanced total vascular surface and luminal diameter and reduced vessel density, from decidual secretory endometrium to decidua parietalis to decidua basalis. The reduced vascular density at the implantation site has been described before in rats and was suggested to result from oedema. However, the vascular density still differed after correction for oedema. The increase in luminal diameter may represent an adaptation to increased blood flow or may be due to vasodilatation reported to occur before infiltration of endovascular trophoblasts. The enlargement of the total vascular surface in the decidua has been reported previously and is likely to be functionally related to the increased blood supply required to serve the growing demands of the fetus.

11. (a) T (b) T (c) F (d) T (e) F

The abundant induction of placental growth factor messenger ribonuclear acid and proteins in decidua basalis in general and of placental growth factor and Flt-1 proteins on endothelial cells in particular is remarkable. Placental growth factor, via Flt-1, is able to potently induce angiogenesis resulting in mature and stable vessels. Angiopoietin-1 maintains vessel integrity, decreases vascular permeability and plays a role in endothelial and vascular maturation after vascular endothelial growth factor-A induced neo-vascularization. Transgenic over-expression of angiopoietin-1 in mice results in the development of more complex vascular networks. Vascular endothelial growth factor-A, via its receptor Flt-1, seems to play an active role in trophoblast invasion during human implantation. Angiopoietin-2 is a functional antagonist of angiopoietin-1 and is only expressed at sites of vascular remodelling. Angiopoietin-2 leads to loosening of cell–cell interactions and allows access to angiogenic inducers like vascular endothelial growth factor. Ang-2 and VEGF promote increased vascular permeability, longer vessels, more complex network of vessels and increased amount of sprouting cells. MT1-MMP is the best known MT-MMP and is involved in degradation of extracellular matrix components, cell migration, and generating bioavailability of growth factors. MT1-MMP has received considerable attention as being involved in tumour angiogenesis and has been shown to be able to induce angiogenesis.

12. (a) F (b) F (c) T (d) F (e) T

Intrauterine growth restriction has been induced by relatively high oxygen levels, which cause disturbed expression of angiogenic factors and decreased branching angiogenesis in placental villi. These relative hyperoxic conditions may explain the decreased vascular endothelial growth factor and increased placental growth factor expression found in fetal growth restriction placentas, as both factors are inversely regulated by oxygen. These differential levels of angiogenic factors may further contribute to increased trophoblast invasion and inhibition of endothelial cell growth, resulting in failure of terminal villi formation and insufficient exchange of oxygen and nutrients to the fetus. ‘Miscarriage vascularization’ in the early first trimester resembles the late first-trimester vascularization pattern. This suggests that the vasculature associated with the pathogenesis of miscarriages is maturing too fast. The premature ripening may allow maternal blood into the intervillous space too early in the development of pregnancy, also demonstrated in vivo by Doppler ultrasound imaging. The early onset of maternal circulation could result in increased oxygen levels with subsequent oxidative stress. This could modulate the architecture of vasculature and the expression of peri-cellular proteases and angiogenic factors. Current knowledge suggests that the pathogenesis of pre-eclampsia starts with defective vascular remodelling of maternal spiral arteries leading to non-invasion of trophoblasts, placental insufficiency and ischaemia. Pre-eclamptic placental bed biopsies show failure of extravillous trophoblasts invasion into the walls of spiral arteries, despite adequate interstitial extravillous trophoblasts invasion. The diseased placenta releases soluble anti-angiogenic factors, such as soluble flt-1 (sFlt-1) and endoglin (sEng). These factors alter the angiogenic balance, mainly by neutralizing vascular endothelial growth factor-A and placental growth factor, induce systemic endothelial dysfunction and finally clinical pre-eclampsia. Overall, more angiogenic activity is generated in the decidua of miscarriages. Earlier, differential antigen expression of vascular endothelial growth factor and its receptors are described in correlation with miscarriages.

13. (a) F (b) T (c) T (d) F (e) F

Screening based on maternal risk factors and history, such as age and family history of pre-eclampsia, will identify 60% of women as being high risk but only 30% of those who will actually develop pre-eclampsia. As our obstetric population becomes more complicated, with older and more obese women, this method becomes ever more unsatisfactory. A review of 19 studies in 2002 showed an overall sensitivity of second trimester Doppler of 55%, although considerable variation existed between studies. The likelihood ratio incorporates the sensitivity and specificity of the test, and provides a direct estimate of how much a test result will change the odds of having a disease. The likelihood ratio for a positive result (LR+) shows how much the odds of the disease increase when a test is positive. The likelihood ratio for a negative result (LR−) shows how much the odds of the disease decrease when a test is negative. As the incidence of pre-eclampsia in the developed world is relatively low (1–3%), a high positive LR and low negative LR are needed for any satisfactory screening test. No individual biomarkers currently have a satisfactory screening performance in isolation.

14. (a) T (b) T (c) F (d) F (e) T

This is thought to be a reflection of impaired placentation, as both these peptides are derived from the syncytiotrophoblast. As they seem to reflect the same aspect of placental function the use of both biomarkers, together may not add additional predictive value compared with either alone. Most studies suggest that the levels of the potent anti-angiogenic factors sFlt 1 and sEng do not seem to be altered until the second trimester. Several studies have shown that first-trimester levels of the pro-angiogenic factor PlGF are reduced in women who subsequently develop pre-eclampsia.

15. (a) F (b) T (c) F (d) F (e) T

In several large, well-conducted trials, no benefit in antioxidant supplementation was shown in either low- or high-risk women. The PARIS study group found that aspirin produced a small but significant reduction in the risk of developing pre-eclampsia. No additional benefit was found in a higher dose regimen than 75 mg or in starting aspirin before 20 weeks. Calcium seems to afford a significant reduction of pre-eclampsia in women with low dietary intake. Smaller reductions were seen in women with adequate intakes. The largest study to date of over 8000 women with low intake, however, failed to show a significant reduction, although it did show a reduction in the serious complications of pre-eclampsia. Younger women aged under 20 years benefitted most, with a number needed to treat of 45 to prevent one serious complication of pre-eclampsia compared with 125 for older women.

16. (a) T (b) T (c) T (d) T (e) F

Women with recurrent pre-eclampsia are more likely to develop severe pre-eclampsia compared with primiparous women, and they also have a higher risk of preterm deliveries, abruption of the placenta and fetal death caused by pre-eclampsia. Recurrent pre-eclampsia seems to reflect a more severe condition compared with first-time pre-eclampsia, and the recurrence risk is inversely related to gestational age at first delivery. A high BMI has consistently been found to increase pre-eclampsia risk, with reported odds ratios between 3 and 5 in obese (BMI >30) compared with normal weight women. However, it seems that the increased risk associated with a high maternal BMI is primarily true in mild or moderate pre-eclampsia (mostly late-onset), and not with severe (early onset) pre-eclampsia. Primiparous women are known to be at increased risk of pre-eclampsia, and pre-eclampsia is considered a condition of first pregnancy. A normal first pregnancy is associated with a greater than 50% reduced risk in a subsequent pregnancy. Immune maladaptation has been suggested as an explanation for effect of parity but, to date, no studies have found evidence of such maladaptation. Smoking in pregnancy has repeatedly been associated with a reduced risk of pre-eclampsia in primiparous and multiparous women, singleton and multifetal pregnancies, and for mild and severe pre-eclampsia. Typically, the relative risk is about 0.5 to 0.8 compared with non-smokers. However, although smoking reduces the incidence, it has been associated with unfavourable fetal outcomes in pregnancies complicated by pre-eclampsia.

17. (a) F (b) F (c) T (d) F (e) F

Fish oil has been shown to lower blood pressure but has not been shown to prevent pre-eclampsia. Vitamin C and E, as antioxidants were once seen as likely to help in the prevention of pre-eclampsia, but several studies have not shown benefit. Low-dose aspirin in some trials has been shown to be of some value in the prevention of pre-eclampsia. It seems to be of most benefit in those women at highest risk for the development of pre-eclampsia. Diuretics and other antihypertensive agents have not been shown to be of any benefit in the prevention of pre-eclampsia. Some evidence shows that antidepressant use during pregnancy may increase rates of pre-eclampsia. There is no evidence that it helps to prevent the disease.

18. (a) F (b) T (c) F (d) F (e) F

Increased diastolic flow is not considered to be predictive of pre-eclampsia. Decreases in diastolic flow are of concern. Diastolic notching, both unilateral and bilateral, is associated with the development of pre-eclampsia. Increased resistance index and increased pulsatility index have been shown to be associated with the development of pre-eclampsia, not decreased values of these parameters. A peak systolic velocity greater than 1.5 MoM in the middle cerebral artery has been shown to be associated with fetal anaemia in allo-immunised fetuses. This parameter is not used in the prediction of pre-eclampsia.

19. (a) F (b) F (c) T (d) F (e) F

C is the only correct answer. An adequate screening test for pre-eclampsia and IUGR is not currently available and is an area of active research. In a recent meta-analysis, treatment with aspirin in women at high risk for pre-eclampsia and IUGR at less than 16 weeks was shown to decrease the incidence of these disorders, whereas later treatment did not have this protective effect. Increased (as opposed to decreased) placental resistance is characteristic of the placentas of pregnancies complicated by pre-eclampsia and IUGR. Abnormal trophoblast-mediated modification of the spiral arteries has been reported with pre-eclampsia even in the absence of IUGR.

20. (a) F (b) T (c) F (d) F (e) F

B is the only correct answer. Second-trimester uterine artery Doppler (not first trimester) has increased sensitivity in the prediction of pre-eclampsia and IUGR, although the sensitivity is too low to warrant its use in screening low-risk populations. Uterine artery Doppler provides an indirect (as opposed to direct) measurement of placental vascular resistance, as the elevated resistance begins with abnormal spiral artery formation. Although the presence of a diastolic notch on uterine artery Doppler is common in early pregnancy, this finding in the third trimester has been correlated with increased (not decreased) risk for pre-eclampsia. The ease of application and good inter- and intra-observer variability made uterine artery Doppler a desirable method for potential screening; however, actual detection rates using the technique have been disappointing and thus limited its utility.

21. (a) F (b) F (c) T (d) F (e) F

C is the only correct answer. Spiral artery spectral Doppler is feasible in early pregnancy, but elevated indices of resistance have not been shown to be sensitive to the prediction of pre-eclampsia and IUGR. The spiral artery Doppler waveform has a much smaller systolic peak and systolic to diastolic ratio compared with the uterine artery Doppler. The only study that showed increased resistance index in women who developed adverse outcomes with pregnancy-induced hypertension or IUGR was carried out in the third trimester, whereas all of the earlier studies showed extremely poor sensitivity for the development of adverse outcomes.

22. (a) T (b) F (c) T (d) T (e) T

Standardised ultrasound settings for the 3DPD have not been published and should be high on the research agenda for this area of research. All of the other statements are correct.

23. (a) T (b) T (c) F (d) T (e) T

The spiral arteries have a myometrial segment and a decidual segment. Failure of physiological transformation of the myometrial segment is the lesion considered typical of disorders of deep placentation. Therefore, sampling of the myometrial segment is required to diagnose these disorders. The decidual segment of the spiral arteries can be visualized by studying the basal plate of the placenta, but this method is not adequate to examine the myometrial segment of the spiral arteries. Hysterectomy specimens can also be used, but in practice, such specimens are rarely available. The uterus allows complete examination of the uterine circulation, including myometrial and decidual segments.

24. (a) F (b) T (c) F (d) F (e) F

Once a placental bed biopsy is obtained at the time of Caesarean delivery or transvaginally, the next step is to determine whether the specimen was truly obtained from the placental bed. This can be done by identifying trophoblast in the specimen. In practice, this is accomplished by staining with cytokeratin, as trophoblast cells are positive for cytokeratin. A placental bed biopsy may have interstitial trophoblasts; yet, the identification of failure of physiological transformation requires the presence of a decidual vessel. Other stains are used to detect smooth muscle (actin) and fibrinoid (PAS). Macrophages and uterine natural killer cells are important components of the decidua, but are not essential to diagnose whether a specimen comes from the placental bed.

25. (a) T (b) F (c) T (d) F (e) F

This question reflects the results of the only study that has examined failure of physiological transformation in the myometrial and decidual segments of the spiral arteries.

26. (a) T (b) T (c) T (d) T (e) F

Failure of physiological transformation of the myometrial segment of the spiral arteries was originally described in pre-eclampsia and intrauterine growth restriction. However, the data presented in this article indicates that defective transformation is present in patients with second trimester spontaneous abortion, preterm labor with intact membranes, prelabor rupture of membranes and abruptio placentae. Currently, there have been no studies examining the frequency of failure of physiological transformation of the spiral arteries in unexplained fetal death.

27. (a) T (b) T (c) T (d) T (e) T

Successful implantation is the end result of a complex molecular dialogue between a receptive, hormonally-primed uterus and a mature, activated blastocyst. Although the molecular and cellular mechanisms responsible for implantation are not well understood, it is clear that multiple signals are needed to synchronise blastocyst maturation and uterine receptivity, including sex steroid and peptide hormones, growth factors, cytokines and immunological factors. Abnormalities in one or more of these factors can lead to pregnancy failure (miscarriage) or defective implantation, with resultant downstream clinical complications (such as pre-eclampsia or preterm labour).

28. (a) T (b) F (c) F (d) T (e) F

Concentrations of endogenous prostaglandins in human decidua are indeed lower in pregnancy than in the endometrium at any stage of the menstrual cycle. This is primarily caused by a decrease in prostaglandin synthesis and not increased metabolism. Moreover, an inability to suppress decidual prostaglandin production around the time of implantation has been associated with early pregnancy loss. Taken together, these data suggest that pregnancy is maintained by a mechanism that tonically suppresses uterine prostaglandin synthesis throughout gestation. As endometrial prostaglandin production is down-regulated also in ectopic pregnancy, it seems likely that systemic rather than local mediators are involved.

29. (a) T (b) T (c) T (d) F (e) F

The most likely candidate for this regulation is progesterone. Progesterone receptor antagonists, such as RU 486, readily induce miscarriage if given before 7 weeks of gestation. Similarly, surgical removal of the corpus luteum, the source of progesterone in the first trimester, results in spontaneous pregnancy loss. These data suggest that adequate progesterone production by the corpus luteum is critical to the maintenance of pregnancy until the placenta takes over this function at around 7–9 weeks of gestation.

The mode of action of progesterone is not well understood, but seems to be partially independent of interaction with either progesterone or glucocorticoid receptors. It is likely that progesterone acts to decrease endometrial prostaglandin production both directly by inhibiting the release of arachidonic acid from endometrial cells and indirectly by up-regulating inhibitors of prostaglandin synthesis. Progesterone may also act by altering prostaglandin receptor activity.

30. (a) F (b) T (c) T (d) T (e) T

The presence in the decidua of two endogenous inhibitors of prostaglandin production that may be important in implantation have recently been identified, namely secretory component and surfactant protein-A (SP-A). The rate-limiting step in the synthesis of prostaglandins of the two-series is the hydrolysis of non-esterified (free) arachidonic acid from membrane phospholipid. This release is mediated by the phospholipase family of enzymes, primarily phospholipase A ₂ (PLA ₂ ). In 1985, Wilson et al. identified an endogenous inhibitor of PLA ₂ in the amniotic fluid of women in the third trimester of pregnancy, and called this compound ‘gravidin’. Subsequent studies have shown that gravidin is the fetal homologue of adult secretory component of the polymeric immunoglobulins, IgA and IgM. Secretory component is a 58-kD glycoprotein that binds to IgA and IgM on the abluminal surface of epithelial glandular cells, transports them across the glands, and is released into the exocrine secretions covalently bound to immunoglobulin. In its unbound (free) form within endometrial glandular cells, however, secretory component, like gravidin, is able to inhibit PLA ₂ activity. Both secretory component and prostaglandin production have been localised primarily to glandular epithelial cells in the decidua, and have shown that progesterone stimulates secretory component expression in these cells, resulting in a rapid and profound downregulation of arachidonic acid release and prostaglandin production. As progesterone production by the corpus luteum is maintained through human chorionic gonadotrophin release by the syncytiotrophoblast, this may provide a mechanism whereby the blastocyst maintains early pregnancy. SP-A may also play a key role in this process. SP-A seems to exert this effect by binding directly to the cytoplasmic protein, peroxiredoxin 6, which has endogenous PLA ₂ activity. The role SP-A in human implantation and placentation has yet to be fully delineated.