40 Christine I. Ekechi and Catriona M. Stalder Queen Charlotte’s and Chelsea Hospital, Imperial College Healthcare NHS Trust, London, UK Spontaneous miscarriage is responsible for considerable emotional and psychological trauma for patients. Recognizing and addressing this issue allows doctors to improve patient care. In the UK this has led to the development of early pregnancy units providing dedicated care for these women. These units also improve clinical care from a diagnostic and management standpoint. In the UK, early pregnancy complications rarely result in maternal death. The triennial report (2005–2007) reported one maternal death from spontaneous miscarriage, although there were 18 direct deaths from maternal sepsis including deaths in early pregnancy [1]. With the advent of commercially available, sensitive and affordable pregnancy tests, women present at increasingly earlier points in pregnancy looking for reassurance and confirmation of viability. It is important that while their anxiety is recognized, we proceed along safe and accepted diagnostic pathways to avoid misdiagnosis. It is also important to recognize that pregnancy is a dynamic process and that a diagnosis of viability early on in the first trimester does not necessarily signify that the pregnancy will continue, although if a fetal heart pulsation is detected at 6 weeks, there is a 90% chance that the pregnancy will continue beyond the first trimester [2]. The rate of miscarriage varies depending on the gestation of pregnancy and maternal age (Fig. 40.1). Up to 50% of early pregnancies will fail within 4 weeks from the last menstrual period (LMP), so‐called biochemical pregnancies. By 6 weeks’ gestation, the rate is one in five pregnancies and by the second trimester that has fallen to 1 in 40 [3]. Simple scoring systems and models exist that can help advise women on the likely viability of their pregnancy using both clinical and ultrasound information [4]. Fig. 40.1 Estimated rates of fetal mortality by weeks of gestation [1]. Spontaneous miscarriage is defined as the spontaneous loss of a pregnancy prior to viability, taken legally in the UK as 23 weeks and 6 days of gestation. Beyond this gestation, fetal demise is classified as a stillbirth. The majority of first‐trimester miscarriages occur below 12 weeks’ gestation with an overall rate of around 20%. Second‐trimester miscarriages are less common, accounting for 1–4% of all miscarriages [5]. While some second‐trimester miscarriages can be explained as first‐trimester losses where the diagnosis is only made in the second trimester, it seems likely that the causes are different. Terminology has moved away from the word ‘abortion’, which is firmly associated with therapeutic abortion among the general public. The importance of accurately defining the different types of miscarriage is that it provides the bedrock upon which comparative research can be built, to better understand the relative benefits and outcomes of treatment options (Table 40.1). Table 40.1 Definitions of terms in common usage. * Extreme caution needs to be taken before making this diagnosis as it can be easy to mistake a parous os (external os open as a result of previous vaginal delivery) and the open cervix of inevitable miscarriage. It is a term probably best avoided. † This is an ultrasound‐based classification and not a diagnosis in itself. Further investigations may reveal an intrauterine pregnancy, an ectopic pregnancy or a miscarriage. The definitions can be seen to be a mixture of clinical and ultrasound‐based diagnoses and are often suggested prospectively and confirmed retrospectively. Care must be taken when relying solely on a clinical diagnosis because this is often refuted by ultrasound. For example, in cases where the clinical picture suggests complete miscarriage, there will be ultrasound evidence of retained products in 45% of patients [6]. Although the causes of miscarriage in the first and second trimester appear different, there is inevitably some overlap, in addition to the occasional situation where diagnosis of a first‐trimester miscarriage is delayed until the second trimester. Evidence suggests that a significant proportion of miscarriages result from chromosomal and genetic abnormalities. It is likely that abnormal implantation has a role to play in some cases and this is an area of current research. It is thought that up to 95% of chromosomally abnormal embryos result in miscarriage [7]. The following chromosomal abnormalities are associated with miscarriage. Other causes implicated in first‐trimester miscarriage include the following. General examination to assess the immediate well‐being of the patient is mandatory. Young women can mask blood loss and significant decompensation is a late sign and therefore attention should be given to more than just blood pressure, for example tachycardia and/or a raised respiratory rate. Pallor, a reduced conscious level or reduced capillary return are all important. It is useful to note that peritoneal distension may also result in bradycardia. Vaginal examination will reveal whether the cervix is open or if products of conception are identifiable at the cervical os. If so, the relevant tissue should be removed and sent for histopathological diagnosis, as on rare occasions a decidual cast (in the presence of an ectopic pregnancy) can mimic products of conception. Products of conception cannot be confirmed on macroscopic inspection unless fetal parts are seen. Where there is a history of complete miscarriage, 45% of patients will show ultrasound evidence of retained products and up to 6% will have an ectopic pregnancy [9]. Speculum examination of the vagina is also a good opportunity to inspect the cervix and vagina to exclude local causes of blood loss in addition to the quantity of loss at presentation, as patient description can be misleading. Table 40.2 Differential diagnosis. * Remember that the presence of fibroids may give a distorted assessment of uterine size or large body habitus may make this difficult to accurately assess. Hydatidiform mole is a relatively rare but important complication of pregnancy which should be considered in all cases of miscarriage and, where possible, tissue sent for histological confirmation of products of conception and appropriate follow‐up arranged. It is clear, however, that in the presence of spontaneous miscarriage at home that this is not possible. It is likely that in these cases, where there is clinically significant molar change, women will present with ongoing bleeding and the diagnosis considered at this stage. There is no evidence that delay in the diagnosis of molar pregnancy increases the likelihood of molar invasion. Ultrasound has progressed enormously since its first use in pregnancy in 1967. It has a pivotal role in the diagnosis of miscarriage. Transvaginal ultrasound has helped identify the early ultrasonographic features seen in a normal early intrauterine pregnancy (Fig. 40.2). The ultrasound landmarks visible on transvaginal scan are as follows. Fig. 40.2 A viable fetus of 7 weeks’ gestation with amniotic sac clearly visible. Failure to identify these landmarks at the presumed gestational age may not necessarily indicate a miscarriage. Dating in early pregnancy is taken from the first day of the LMP and conception presumed to have taken place on day 15. Clearly this leaves a large window for inaccuracy due to varying cycle lengths, delayed ovulation, variability in the ovulation–implantation window and inaccurate recall of menstrual dates. In the current climate of sensitive urinary pregnancy tests where women are presenting at increasingly earlier gestations with the expectation of reassurance of a viable intrauterine pregnancy, it is imperative that care is given to obtain the correct diagnosis. In these scenarios it may be a number of weeks before a viable pregnancy can be visualized due to natural variation in the appearance of structures and the inevitable uncertainty that surrounds dating. In 2011, new research demonstrated that previously used criteria for the ultrasound diagnosis of missed miscarriage were unsafe, resulting in an unacceptably high false‐positive rate. This implied that a number of pregnancies were being incorrectly diagnosed as missed miscarriages with the potential for the termination of wanted intrauterine pregnancies [10]. Following this, a conference of the Society of Radiologists in Ultrasound in the USA resulted in a consensus paper in the New England Journal of Medicine [11] that proposed sensible guidelines for the diagnosis of pregnancy failure based on the 2011 paper by Abdallah et al. [10]. Subsequently, the UK National Institute for Health and Care Excellence (NICE) [12], the Royal College of Obstetricians and Gynaecologists (RCOG) [13] and the American College of Radiology [14] have all changed their ultrasound criteria for the diagnosis of miscarriage, which are now based on: Fig. 40.3 Ultrasound diagnosis of miscarriage must be based on either a mean sac diameter of ≥ 25mm or an embryo with crown‐rump length (CRL) of ≥ 7mm. Where neither of these criteria has been satisfied on the initial ultrasound scan, the pregnancy should be classified as a pregnancy of unknown viability (PUV) and an ultrasound scan then performed at an interval in order to definitively comment on viability. When considering the optimal interval between ultrasound scans for the diagnosis of miscarriage to be made with certainty, in the study by Preisler et al. [15] a minimal time interval of 7 days was 100% specific for miscarriage where the initial scan identified a pregnancy with an embryo of less than 7 mm with no heart activity or a pregnancy with no embryo and an empty gestational sac with an MSD of 12 mm or more. Where the initial scan identified an empty gestational sac with an MSD of less than 12 mm, a minimal time interval of 14 days was 100% specific for miscarriage if sac size had not doubled. Although the data for these criteria were scanty, this paper also showed that initial scans demonstrating an embryo with a CRL of 3 mm or more with no heartbeat or an MSD of 18 mm or more at 70 days (10 weeks) or older of gestational age was very highly predictive of a missed miscarriage. This has been suggested as a possible new additional criterion to the guidelines for the definitive diagnosis of missed miscarriage [15].
Spontaneous Miscarriage
Definition
Term
Definition
Threatened miscarriage
Vaginal bleeding in the presence of a viable pregnancy
Inevitable miscarriage
Vaginal bleeding in the presence of an open cervical os and pregnancy‐associated tissue still present*
Incomplete miscarriage
Vaginal bleeding that is ongoing where pregnancy tissue has already been passed but ultrasound suggests the presence of further tissue within the uterine cavity
Complete miscarriage
Clinical definition: cessation of bleeding and a closed cervix following miscarriage
Ultrasound definition: an empty uterus with a falling hCG where an intrauterine pregnancy was previously confirmed
Missed miscarriage/early fetal demise
Miscarriage occurring in the absence of symptoms or minimal symptoms, where the empty gestation sac or non‐viable embryo is still visible within the uterus
Recurrent miscarriage
Three or more consecutive early pregnancy losses
Biochemical pregnancy loss
Pregnancy not located on scan where there is/has been a positive pregnancy test which subsequently becomes negative
Empty sac
A gestation sac with absent or minimal structures
Pregnancy of unknown location (PUL)
Positive pregnancy test where the location of the pregnancy is not currently identifiable using transvaginal ultrasonography†
Pregnancy of unknown viability (PUV)
The presence of intrauterine structures confirming the location of the pregnancy, but where no embryo heartbeat has been seen to confirm its viability. By definition the measurements of the embryo or gestation sac do not meet the criteria for the diagnosis of a missed miscarriage. In this circumstance a repeat scan at an interval is required to confirm viability (see section on ultrasound diagnosis)
Aetiology
First‐trimester miscarriage
Second‐trimester miscarriage
Diagnosis
Diagnosis is based on appropriate history‐taking, examination and suitably directed diagnostic tests.History‐taking
Examination
Abdominal palpation
Vaginal examination
Differential diagnosis (Table 40.2)
Uterine size*
Cervix
Blood loss
Pain
Threatened miscarriage
Equivalent to dates
Closed
Any
Variable
Incomplete miscarriage
Smaller than dates
Open
Usually heavy
Present
Complete miscarriage
Smaller than dates
Closed
Previously heavy, now settling
Previously present, now absent
Missed miscarriage
Variable
Closed
Variable
Variable
Diagnostic tools
Ultrasound
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