19. Obstetrics

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Source: CDC, Public domain, via Wikimedia Commons.

19.1 Introduction

When a patient is planning to become pregnant

  • Start folate supplementation (0.4 mg daily).

  • In patients with prior hx of neural tube defects, use higher dose of folate (4 mg daily).

  • Folate supplementation decreases risk of neural tube defects.

Diagnosing pregnancy

  • Most common (MC) presentation is missed menstrual period in a sexually active female.

  • Diagnostic test of choice is qualitative urine pregnancy tests. This detects β-hCG (human chorionic gonadotropin) in the urine.

  • NSIDx is ultrasonography (US) of pelvis. If it shows intrauterine pregnancy, no further diagnostic steps are necessary.

19.2 Pregnancy Terminology and Timeline

19.2.1 Gravida and Parity


Number of pregnancies including current pregnancy.


Number of instances of delivery of viable fetus/es.

1 A mother who has delivered twins is G1P1. Successful twin pregnancy is counted as 1.



First trimester

Weeks 1-12

Second trimester

Weeks 13-27

Third trimester

Weeks 28-till birth

Spontaneous abortion

Loss of pregnancy prior to 20 weeksa

Intrauterine fetal death

Death in utero of fetus >20 weeks

Preterm pregnancy

Delivery between 24 and 36 weeks

Full-term pregnancy

Delivery between 37 and 41 weeks

Postterm pregnancy

Any pregnancy beyond 42 weeks

a20-24 weeks is the cut-off for a potentially viable pregnancy.

Exam tip: For all obstetric questions, categorize gestation into first, second, or third trimester. If third trimester, categorize further into preterm, term, and postterm.

What is gravida and parity in the following situation?

  1. Hx of first-trimester abortion.

  2. Pregnant mother with prior hx of twin delivery


  1. G1PO

  2. G2P1

19.2.2 Dating Pregnancy

Naegele’s rule: It is used to determine the estimated date of delivery (EDD) based on the first day of the last menstrual period (LMP).

EDD = LMP – 3 months and + 7 days

2 If LMP is September 8, 2016, what is the EDD?

EDD = – 3 months and + 7 days

9 – 3 = 6: 8 + 7 = 15

EDD = June 15, 2017

Ultrasound dating:

Pregnancy dating using first trimester US is more accurate than LMP dating. Crown-rump length measurement is used in the first trimester.

3 Crown-rump length.

After the first trimester, use combination of head and abdominal circumference and femur length.

US accuracy falls with the increase in pregnancy duration.

19.3 Physiological Changes in Pregnancy

Pregnancy hormones

  • Soon after fertilization, the embryo starts making β-hCG that signals corpus luteum to continue producing progesterone and estrogen, which maintain uterine lining.

  • After placenta develops, it replaces corpus luteum for the job of supplying progesterone and estrogen to maintain pregnancy.

  • Relaxin, a hormone produced by placenta, plays a role in relaxation of pelvic girdle and cervical dilation in preparation of delivery.


  • Decrease in blood pressure (BP; this is due to vasodilatory properties of female hormones).

  • Increased cardiac output: initially due to increase in stroke volume, and later in pregnancy, as a result of increased heart rate (HR).

  • Increased plasma volume.


  • Increased tidal volume and resultant chronic respiratory alkalosis with metabolic compensation (this is progesterone-mediated).

  • Decreased total lung capacity due to elevation of diaphragm.


  • Morning sickness (typically resolves by 16 weeks).

  • Increased risk of gastric reflux and constipation.


  • Increased renal plasma flow and GFR (glomerular filtration rate).

  • Decreased blood urea nitrogen (BUN)/creatinine (Cr) ratio.

  • Increased urinary frequency.


  • Hyperpigmentation: linea nigra (straight black midline in the suprapubic region), melasma, and hyperpigmentation of the nipples and perineum.

  • Spider angiomata and palmar erythema may develop due to increased estrogen levels.

  • Varicose veins and venous stasis.


  • Increased estrogen and progesterone.

  • Increased human placental lactogen.

  • Increased prolactin.

  • Elevation of “total T4” due to increase in thyroglobulin synthesis (stimulated by estrogen).

  • Slightly lower T3 and FT4 can occur in the latter half of pregnancy.

  • Slightly low or low-normal thyroid-stimulating hormone (TSH) in the first trimester.


  • Dilutional anemia.

  • Hypercoagulable state.


  • Increased lumbar lordosis occurs typically in the latter half of pregnancy and can cause lower back discomfort.

  • Relaxation of ligaments.

19.4 Prenatal Care

Pregnancy time line

Recommended routine/screening tests

What to do?

First visit

  • Blood type: if Rh(D) -ve, do antibody screen (anti-D immunoglobulin screen).

  • CBC (complete blood count) to rule out anemia

  • Rubella and varicella antibody, Venereal Disease Research Laboratory (VDRL)/ Rapid Plasma Reagin (RPR), hepatitis panel, Chlamydia testing, HIV. (All pregnant women should have these tests.)

  • Neisseria gonorrhoeae testing only in women age < 25 or those at risk (multiple sex partners, history of sexually transmitted disease [STD], illicit drug use, etc.)

  • Pap smear, as per schedule

  • Influenza vaccination during flu seasona and TDaP

  • Urine protein and cultureb

  • US to confirm EDD

  • It is reasonable to offer genetic screening for cystic fibrosis to all pregnant patients or couples planning pregnancy (especially to white couples)

If rubella and varicella antibodies are negative, they may be candidates for postpartum immunization.

If VDRL or RPR is positive, NSIDx is specific treponemal testing (e.g., MHA-TP, FTA-ABS)

24-28 weeks

If Rh(D) -ve, repeat antibody screen.

If antibody screen is negative, prevent sensitization (give 300 mcg dose of RhoGAM at 28 weeks’ gestational age [GA]).

One hour oral glucose tolerance test

See in gestational diabetes section

36th-37th week

Group B streptococci (GBS) rectovaginal culture

If positive, give prophylactic intravenous (IV) penicillin during labor

aIf an exam question of routine pregnancy follow-up mentions one of the months in-between October to May, then the likely answer is to give flu vaccination.

bAsymptomatic bacteriuria in pregnancy needs to be treated promptly. Without treatment, it is likely to cause clinical UTI (urinary tract infection), acute pyelonephritis, and various feto-maternal complications (e.g., preterm labor, low birth weight). (!)

DOC is nitrofurantoin. Other antibiotic options include amoxicillin-clavulanate, cephalexin, cefpodoxime (an oral third-generation cephalosporin), or single-dose fosfomycin.

4 Avoid Bactrim in the first trimester and at term.

19.4.1 Prenatal Screening for Common Aneuploidies

Background: Aneuploidy occurs due to abnormal cell division (most commonly due to meiotic nondisjunction). This results in daughter cells having wrong number of chromosomes. The commonly encountered non-sex chromosomal aneuploidies are Down (trisomy 21), Edward (trisomy 18) and Patau syndrome (trisomy 13). Edward and Patau are universally fatal.

Screened population: Pregnant women ≥ 35 years old are offered screening for detection of chromosomal abnormalities. There is a 1/200 risk for any chromosomal abnormality in this age group.


(!) do not choose chorioamnionitis as a complication of asymptomatic bacteriuria in pregnancy, as it is not related to chorioamnionitis.

Screening method: Use the following test as per GA

5 Always look at the GA (gestational age) in a pregnancy related question in exam.



What screening test to offer?

Late first trimester

9-13 weeks

Nuchal translucency (US), free β-hCG, and PAPP-A (pregnancy-associated plasma protein A)a , b

> 10 weeks

Cell-free fetal DNA a : Placental fetal DNAs are present in maternal circulation, which can be used for the detection of chromosomal abnormalities (e.g., trisomy 21, 18, or 13).

Not recommended for sex chromosome aneuploidies due to a high rate of falsepositive results, despite claims of high accuracy in company-sponsored studies.

Early second trimester

10-14 weeks

Chorionic villus sampling (CVS): Removal of a small amount of placental chorionic villi using a transcervical or transabdominal approach under US guidance.

As these are invasive, it is usually performed after noninvasive testing.

15-18 weeks

Amniocentesis involves transabdominal removal of amniotic fluid under US guidance.

15-18 weeks

Quadruple screeninga,b measures maternal serum alpha-fetoprotein (AFP), β-hCG, estriol, and inhibin-A levels.

aIf noninvasive testing is abnormal, NSIM is a thorough US (to confirm GA and to look for anatomic abnormalities). Cell-free fetal DNA testing (for suspected trisomy) can be done. Confirmatory testing, such as chorionic villus sampling or amniocentesis, is done only if abnormal results are found in noninvasive testing.

6 Placental mosaicism can give false-positive results in chorionic villus sampling. As amniocentesis provides fetal cells directly, placental mosaicism is not a problem. Also, chorionic villus sampling has a higher risk of abortion, but its advantage is that it can be done earlier than amniocentesis.

Complications of invasive methods include spontaneous abortion, infection, fetomaternal hemorrhage, and fetal injury.


First trimester testing

Quadruple screening



Nuchal translucency



Unconjugated estriol

Inhibin A

Trisomy 21 (Down syndrome)




Trisomy 18 (Edwards syndrome)






Open neural tube, ventral-wall defects






Multiple gestation





Abbreviation: n/a, not applicable.

19.5 Vaginal Bleeding during Pregnancy

19.5.1 Abortion

Definition: Fetus loss of < 20 weeks’ gestation.

Etiology: The (MCC) spontaneous abortion in the first trimester is chromosomal abnormalities. During the second trimester, etiologies of abortion include infection/teratogen exposure, incompetent cervix, trauma, etc.


Down APE = Down syndrome has low (or down) APE = AFP, PAPP-A, Estriol

Edward low HEAP = Edward syndrome has low HEAP = Hcg, Estriol, AFP and PAPP-A is low Trisomy 13 (Patau syndrome) not included here as the quadruple screening results can be variable. But. PAPP-A is typically low and nuchal translucency is increased.

19.5.2 Types of Abortion

Main differentiating features

Types of abortion


Cervical Os

Pain/ cramping

US findings



Vaginal bleeding or spotting without any cervical changes and a viable fetus.

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Absent or mild

Alive and viable fetus

Reassurance and outpatient follow-up.


Vaginal bleeding and cramping with dilated open cervix, without passage of POC (products of conception).

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POC visualized in uterus

If heavy bleeding, hemodynamic instability or infection, surgical evacuation (D&C) is performed.


Passage of some POC, with some POC remaining in the uterine cavity.

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Some retained POC in uterus

If the above not present, any of the following can be done:

  • Expectant management is reasonable in stable patients. (Here we need to make sure the abortion is complete.)a


  • Medical abortion (use misoprostolb alone or in combination with mifepristonec). Note that medically induced abortion is less effective in late first trimester.


  • Surgical evacuation


Final stage of abortion:

POC completely evacuated from the uterine cavity

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Absent or mild

Empty uterus

Usually no intervention


Death of fetus in utero, with a closed cervix and no passage of POC.

This is equivalent to intrauterine fetal death.e

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Absent or mild

Dead fetus in uterod

Manage as inevitable or incomplete abortiond

aIn management of expectant or medical abortion, some experts recommend follow-up US and/or β-hCG testing until undetectable.

bMisoprostol (a prostaglandin agonist) causes cervical ripening, dilation, and uterine contractions.

cMifepristone (progesterone antagonist) is rarely used alone, probably because the progesterone level in abnormal pregnancy is already low, thus it is less effective.

dIn some cases, there might be an empty gestational sac with no fetal tissue development inside the sac. This condition is known as empty gestational sac (blighted ovum), which presents in a similar manner to missed abortion and is managed the same way. It likely occurs due to spontaneous fetal regression.

eFetal death in utero < 20 weeks of GA (gestation age) = missed abortion; > 20 weeks GA = intrauterine fetal death.


Think of this as the first stage of abortion.


Think of this as the second stage of abortion.

19.5.3 Septic Abortion

Definition: Abortion + intrauterine infection.

Risk factors: Induced abortion, uterine instrumentation, STD, etc.

Presentation: Recent abortion or ongoing active abortion with symptoms of uterine infection (e.g., fever, foul-smelling discharge, uterine tenderness).

Management: Get blood and endometrial cultures, start broad-spectrum antibiotics, and perform emergent surgical evacuation.

19.5.4 Recurrent Abortions

Definition: Three or more consecutive pregnancy losses.

7 For healthy women who had 1-2 spontaneous abortions in the first or early second trimester, no extensive workup is needed.

Potential causes and diagnostic evaluation:

Uterine abnormalities (cervical incompetence, bicornuate uterus, etc.)

Sonohysterography is preferred (transcervical saline infusion into the uterine cavity followed by transvaginal US [TVUS])

  • Other tests, which may be needed, include hysterosalpingography, magnetic resonance imaging (MRI), laparoscopy, hysteroscopy, etc.

Antiphospholipid syndrome

  • Look for hx of deep-vein thrombosis (DVT) or arterial embolism, and elevated activated partial thromboplastin time (APTT).

  • If suspected, NSIDx is to check anticardiolipin antibodies and lupus anticoagulant.

  • Rx: LMWH (low-molecular-weight heparin) throughout pregnancy.

Thyroid disorders

TSH and free T4

Chromosomal disorders

Do cell karyotyping in parents to look for chromosomal abnormalities (translocations, deletions, etc.)


MCC of thrombophilia is factor V Leiden.

19.5.5 Cervical Incompetence


Cervical tissue trauma

Hx of forceful delivery, multiple gestation, dilation and curettage, etc.

Cervical tissue removal

LEEP (loop electrosurgical excision procedure), cone biopsy, etc.

Collagen disease

Ehlers-Danlos syndrome

Uterine abnormalities

  • Diethylstilbestrol (DES) exposure

  • Congenital conditions

Pathophysiology: Weak cervix may not be able to support the enlarging fetus and increasing uterine pressure, leading to preterm prelabor rupture of membranes and preterm labor.

Presentation: Painless cervical dilatation typically in the latter half of pregnancy. Exam may reveal membranes bulging into vagina. Management:

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aCervical cerclage (bands or suture) is placed at 12-14 weeks and removed at term (37th week).

bProgesterone is started at 16-20 weeks and continued until 36 weeks of pregnancy.

cStart TVUS at 14-16 weeks and end screening at 24 weeks.

Exam tip: Know the timing of various interventions.

Abbreviation: TVUS, transvaginal ultrasound.

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19.5.6 Ectopic Pregnancy

Definition: Any pregnancy that occurs outside of the uterus.

8 MC location is fallopian tube.

Risk factors: Sexually transmitted diseases (STDs), pelvic inflammatory disease (PID), Intrauterine devices (IUDs), tubal ligation, etc.

Presentation: Abdominal pain, lower abdominal tenderness ± vaginal bleeding ± hx of amenorrhea. Ruptured ectopic pregnancy can present with hemodynamic instability due to bleeding and hypovolemic shock.

9 Any woman of reproductive age presenting with abdominal pain should be evaluated for ectopic pregnancy.

Diagnosis: Pelvic exam may reveal a palpable, tender mass (can be absent in ruptured ectopic pregnancy), cervical motion tenderness, and/or adnexal tenderness ± gross bleeding.


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aIf transabdominal US is negative, NSIDx is TVUS.

10 In early pregnancy, transabdominal US may not reveal an intrauterine sac, so use TVUS.

bThis cut-off of β-hCG ( >1,500-2,000 mIU/mL) is used because at this β-hCG level, TVUS should be able to visualize intrauterine pregnancy.

cIn intrauterine pregnancy, β-hCG levels rise by ≥35% by every 2 days.

dIn stable patients with unruptured ectopic pregnancy, treatment may be surgical (laparoscopy) or medical (methotrexate or similar agent). If medically managed, closely follow β-hCG levels. If β-hCG is not trending down, a second round of methotrexate dose can be given. If still not responding, NSIM is laparoscopy.

Abbreviations: TVUS, transvaginal ultrasound; US, ultrasound.

19.5.7 Third-Trimester Bleeding


Key features


Placenta previa

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Abnormal placental implantation in the lower uterine segment, overlapping the cervical os:

  • Partial placenta previa: Covers a portion of the internal cervical os.

  • Complete placenta previa: Covers the entire surface of the internal cervical os.

MC risk factor: Scarring as a result of previous cesarean delivery

Presentation: Painless bleeding in third trimester (bleeding occurs due to separation of anchoring villi in the lower uterine segment).

  • The following are contraindicated due to risk of bleeding: digital vaginal exam, intercourse, excess physical activity, and vaginal delivery.

  • When low-lying placenta is seen in the first or second trimester, NSIM is abdominal US in the third trimester. Usually as the uterus stretches, placenta migrates upwards.

  • If persistent in the third trimester, schedule cesarean section at 36-37 weeks.

  • For acutely bleeding patients, NSIM is hospitalization and close fetomaternal surveillance. In < 34 weeks’ pregnancy, expectant conservative management is appropriate (give steroids too). If > 34 weeks, cesarean delivery is indicated.

Placental abruption aka abruptio placenta

  • Look for retroplacental clot.

This occurs when a portion of the placenta prematurely separates from the uterine wall.

Risk factors:

  • Chronic pathologic vascular processes such as hypertensive disorders of pregnancy, cigarette smoking, maternal old age, etc.

  • Can also occur due to trauma,a acute vasoconstriction (such as cocaine use), or sudden decompression (such as polyhydramnios with rupture of membrane)

Presentation: Presents beyond 20 weeks with painful bleeding, abdominal and back pain.

If hematoma is contained within the uterine cavity, there may be no frank bleeding.

  • Large separation leads to decreased oxygen delivery to fetus (this can be detected by abnormal heart tracing).

  • Maternal complications include hemorrhagic shock, disseminated intravascular coagulation (DIC), and Couvelaire uterus.b

  • Chronic abruptio placenta can result in intrauterine fetal growth restriction (IUGR), oligohydramnios, and pre-eclampsia.

NSIDx is abdominal US.

  • First step is continuous fetal and maternal monitoring and supportive management (blood products and/or IV fluids as needed).

  • If maternal or fetal instability, prompt delivery is indicated (cesarean section, if vaginal delivery is not imminent) + aggressive supportive treatment.

  • If mother and fetus are stable and no evidence of worsening abruption, look at the GA (gestational age):

    • In < 34 weeks’ pregnancy, expectant conservative management is appropriate (give steroids too).

    • If > 34 weeks, delivery is indicated.

Placenta accreta/increta and percreta

  • Placenta normally should be attached only to decidua, so it can easily separate from uterine wall after delivery.

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Source: TheNewMessiah at English Wikipedia, Public domain, via Wikimedia Commons.


• Accreta is when placental villi attach to myometrium.

• Increta is when it invades myometrium.

• Percreta is when it penetrates the myometrium to reach the serosa and into the peritoneal cavity. If it invades the bladder, it might cause hematuria.

Risk factors: MC risk factor is placenta previa with hx of cesarean delivery; other risk factor includes prior uterine surgery (such as myomectomy)

Presentation: Placenta fails to delivery spontaneously and when manual placental separation is attempted, profuse massive bleeding occurs (morbidly adherent placenta).

• Best case scenario is when it is discovered during a screening US.

• Elective hysterectomy with cesarean section is recommended in most cases, at 34-36 weeks with predelivery steroids. Rarely, if further childbearing is desired, uterus conservation may be attempted (e.g., placental resection).

• If discovered during cesarean delivery, NSIM is hysterectomy (cannot risk trying to remove placenta because of risk of massive hemorrhage).

Uterine rupture

Risk factors: Uterine scarring (due to prior cesarean deliveries—particularly vertical cesarean section, or myomectomy), multiple gestation, trauma, excessive use of oxytocin during labor, etc.

Presentation: Typically presents with sudden acute pain, signs of fetal distress, and the fetal-presenting part may withdraw into the abdomen (loss of fetal station). Most often occurs during labor.

Emergent surgery with cesarean delivery, followed by either hysterectomy or repair (in women who desire further pregnancies).

Vasa previa

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Description: Aberrant fetal vessel near the cervical os

Presentation of bleeding: Painless bleeding with significant fetal distress. Pulsating vessels may be palpated on clinical exam.

All women with low-lying placenta or placenta previa should get screening for vasa previa with TVUS and Doppler flow assessment.

If found to have vasa previa, schedule cesarean section at 34-37 weeks.

aWhen pregnant patients present with hx of significant trauma in late-pregnancy, NSIM is close fetomaternal surveillance and US.

bThis is when the retroplacental hemorrhage penetrates the myometrium. The uterus becomes atonic, very painful, and prone to severe postpartum bleeding. This may progress to bleeding into the peritoneal cavity.

  • All of the above can present with bleeding during labor. Placenta previa can have abdominal pain and bleeding, but is usually mild to moderate. Severe pain points toward abruptio placenta or rupture, but these can also present with mild to moderate pain. So, an important differentiating factor is US (ultrasound).

  • Look for loss of fetal station in uterine rupture.

  • Normal delivery does not have vaginal bleeding; however, there may be the passage of a small amount of blood or blood-tinged mucus through the vagina near the end of pregnancy (which is called the bloody show).

  • Also look for management of Rh(D) incompatibility.

19.5.8 Rhesus (Rh) Incompatibility

Rh(D) is an antigen found in RBCs. Most people are Rh(D) +ve, but some people can be Rh(D) negative. When an Rh(D)-negative person is exposed to Rh(D) +ve RBCs, this will stimulate production of anti-Rh(D) antibodies. Exposure to Rh(D) antigen occurs with incompatible blood donation (which rarely occurs), or when the Rh(D)-negative female is pregnant with an Rh(D) +ve fetus and there is fetomaternal hemorrhage.

Immunoglobulin G (IgG) antibodies against Rh(D) produced as a result of exposure to Rh(D) +ve antigen is called Rh(D) sensitization (alloimmunization). These IgG antibodies can cross the placenta and cause hemolytic disease of the fetus and newborn.

Screening for antibody:

All pregnant patients who are Rh(D) -ve

Screen for antibody:

  • During the initial prenatal visit

  • At 24-28 weeks’ GA (gestational age)

  • After delivery

If Rh(D) antibody is -ve

Prevention of sensitization (alloimmunization) is important; use RhoGAM (anti-RhD immunoglobulin) when indicated.

If Rh(D) antibody is +ve

Fetus is at risk for hemolytic diseases of newborn.

There is no use of giving RhoGAM to already alloimmunized patient.

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Dec 11, 2021 | Posted by in OBSTETRICS | Comments Off on 19. Obstetrics

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