Prenatal care

Prenatal care refers to the healthcare that women receive throughout pregnancy. Guidelines for routine prenatal care determine the scope and frequency of prenatal visits and screening. Prenatal visits aim to detect high-risk pregnancies and to monitor the course of pregnancy and fetal development. They involve recording the mother's medical history, consultations, physical and gynecological examinations, laboratory diagnostic analyses, and regular ultrasound screening. Prenatal care visits initially occur once monthly until the 28^th week of gestation, twice monthly between the 28^th and 36^th week, and weekly after the 36^th week. This article covers the general principles of prenatal care, as well as some of the most important diagnostic methods routinely used for the care of pregnant women (i.e., Leopold's maneuvers, obstetric ultrasound).

Frequency of check-ups

• Until the 28^th week of pregnancy: monthly
• From the 28^th week until the 36th week: every two weeks
• From the 36^th week until birth: every week
• In high-risk pregnancies, frequent visits are usually warranted.

Initial examination (∼ 10 weeks of gestation) ^[1]

• Personal and family history, previous pregnancies
• Gynecological examination
• Blood pressure
• Weight
• Laboratory analysis: standard laboratory tests performed in all pregnant women during the first prenatal visit
  • Complete blood count
  • Hemoglobin: screening for anemia (often iron deficiency anemia)
  • Blood typing (ABO and rhesus): screening for risk of hemolytic disease of the newborn
    • Rhesus negative mothers: prophylactic anti-D immunoglobulins at 28 weeks to prevent alloimmunization
  • Urine dipstick protein testing: screening for proteinuria (baseline value is vital for comparison with results in later pregnancy to rule out preeclampsia); performed during every prenatal visit
  • Urine culture: screening for asymptomatic bacteriuria (see treatment of urinary tract infections in pregnant women)
  • Screening for STIs
    • HIV testing (see HIV in pregnancy): all pregnant individuals
    • Syphilis screening (see Syphilis during pregnancy): all pregnant individuals
    • Hepatitis B surface antigen testing (see hepatitis B testing and hepatitis B in pregnancy): all pregnant individuals
    • Hepatitis C screening (Anti-HCV antibody testing): all pregnant individuals
    • Prenatal gonorrhea screening: in all patients < 25 years of age and ≥ 25 years with high risk of infection
    • Prenatal screening for Chlamydia trachomatis
      • In all patients < 25 years of age and ≥ 25 years with high risk of infection (according to CDC and US Preventive Services Task Force guidelines)
      • In all pregnant patients (according to the ACOG guidelines)
  • Rubella and varicella antibody testing (unless there is evidence of immunity)
• PAP smear
• Ultrasound assessment of the estimated gestational age through the crown-rump length (see also diagnosis of pregnancy)
• General advice for pregnant women
  • Vaccination against seasonal influenza recommended to all women
  • Nutritional recommendations during pregnancy are also provided (see nutrition during pregnancy)
  • Tdap vaccine during the 3^rd trimester of every pregnancy to provide fetal immunity to pertussis

Subsequent examinations

The following should be performed during each prenatal care visit regardless of pregnancy-related complaints and symptoms:

• Weight monitoring: to avoid fetal developmental problems (if weight gain is less than the recommended amount), fetal macrosomia, or maternal obesity (if weight gain is above normal)
• Blood pressure monitoring: early detection of pregnancy-induced hypertension
• First-trimester screening; : battery of tests for the screening of chromosomopathies
• Physical examination
  • Fundal height and position of the fetus (identified through the first Leopold maneuver)
  • Fetal heart monitoring (via ultrasound or cardiogram)
• Laboratory
  • Prenatal screening for Group B streptococcus performed between 36 0/7 and 37 6/7 weeks of gestation (vaginal and rectal swab for culture and gram staining) because colonization by this bacteria may cause chorioamnionitis and neonatal infection.
  • Repeat Hb from the 24^th week of pregnancy.
  • 50-g, one-hour oral glucose challenge test (initial screening) at 24–28 weeks gestation
  • 100-g, three-hour oral glucose tolerance test (oGTT) to confirm diagnosis in case of positive initial screening
  • Repeat rhesus screening: An unsensitized Rh(D)-negative women should receive anti(D)-immune globulin (see anti-D prophylaxis).

• All pregnant women (regardless of age) should be offered noninvasive aneuploidy screening tests (before 20 weeks of gestation)
• Possible tests
  • Testing maternal serum; : measurement of specific biomarkers and ultrasound markers that indicate an increased risk for aneuploidy
  • Cell-free fetal DNA testing
• All pregnant women (regardless of age) should be given the alternative option to undergo invasive genetic testing (amniocentesis or chorionic villus sampling)
• Pre-test counseling must be provided: inform the parents that screening is voluntary; explain the difference between screening and diagnostic tests, risk of false positive and false negative tests, explain option of terminating the pregnancy if aneuploidy is diagnosed

Noninvasive screening tests ^[2][3]

First trimester combined screening test

Quad and triple screening tests

AFP is interpreted based on the fetal gestational age. The most common cause for an abnormal AFP in maternal serum is an inaccurate fetal gestational age.

Invasive diagnostic tests

Four abdominal palpation maneuvers used during physical examination to determine the presentation, position, and engagement of the fetus in utero.

• First: bimanual examination of the fetal position; (longitudinal/oblique/transverse) and fundal height
• Second: bimanual examination of the location of the fetal back (i.e., either on the mother's left or right side)
• Third
  • One hand grasps above the symphysis in an attempt to determine if the presenting part of the fetus is engaged.
  • In cases of cephalic presentation , the fetal head feels hard and ballotable; if the fetus is in a breech position, a soft and less movable rump can be felt.
• Fourth: : Bimanual determination of the location of the fetal brow and the degree of flexion of the fetus's head. Usually performed during the later stages of pregnancy when the fetus has entered the pelvic inlet.

References:^[5][6][7]

The following tests are performed in high-risk pregnancies to assess the risk of antenatal fetal death.

• Nonstress test (NST): a noninvasive test (CTG) that measures FHR reactivity to fetal movements
  • Indications: maternal medical conditions (e.g., gestational diabetes, preeclampsia) or fetal conditions (e.g., fetal heart defects, fetal growth restriction)
  • Usually performed in the third trimester (after the 32^nd gestational week)
  • Interpretation
    • Reactive nonstress test: A normal NST that shows ≥ 2 FHR accelerations.
      • Uncomplicated pregnancy: reassurance and discharge
      • High-risk conditions: perform weekly nonstress tests
    • Non-reactive nonstress test: if the NST is nonreactive (<2 FHR accelerations)
      1. Perform vibroacoustic stimulation and record the NST for another 20 minutes
      2. If the NST is still non-reactive: check the biophysical profile (BPP) or perform contraction stress test
    • Category II fetal heart rate tracing
      • A fetal heart rate pattern that is neither normal nor definitively abnormal
      • Requires close monitoring, due to varied potential for developing fetal acidosis and hypoxia
• Contraction stress test (CST): measures FHR reactivity in response to uterine contractions
• Biophysical profile (BPP): a noninvasive test that evaluates the risk of antenatal fetal death, usually performed after the 28^th gestational week
  • Measured parameters: each parameter receives a score of either 0 (abnormal) or 2 (normal) points (see table below).
    • Ultrasound exam
      • Fetal movement
      • Fetal tone
      • Fetal breathing
      • Amniotic fluid volume
    • NST (optional, not always performed)
  • Interpretation
    • Total score ≥ 8 points: no signs of fetal compromise at the time of testing → reassurance
    • Total score 5–7 points: unclear risk of fetal compromise → repeat BPP within 24 hours
    • Total score ≤ 4 points: potential fetal compromise → delivery is indicated (if pregnancy duration is < 32 0/7 weeks, administer steroids and continue close monitoring)

References:^[9][10]

Standard examinations

First-trimester ultrasound ^[11]

Typically performed transvaginally around 6–8 weeks' gestation.

• Evaluate the presence and location of the pregnancy (e.g., intrauterine or ectopic pregnancy).
• Determine the number of fetuses.
• Confirm gestational age (due date).
• Document crown-rump length and cardiac activity.
• Screen for abnormalities of the cervix, uterus, and placenta.

Second- or third-trimester ultrasound

Typically performed transabdominally around 18–22 weeks' gestation.

• Evaluate fetal presentation.
• Evaluate number of fetuses.
• Evaluate fetal anatomy and growth.
• Estimate amniotic fluid volume.
• Evaluate placental position (e.g., to rule out placenta previa).

Additional examinations

In case of high-risk pregnancies or complications during pregnancy (e.g., premature rupture of membranes or bleeding during pregnancy), additional ultrasound exams should be performed.

• Ultrasound-guided first trimester genetic screening: to guide needle placement in amniocentesis or chorionic villus sampling
• Ultrasound for cervical cerclage placement: in cervical insufficiency
• Ultrasound-guided external cephalic version: to turn a breech baby before labor
• Doppler ultrasound
  • Indications
    • Suspected fetal growth restriction (see “Doppler velocimetry of the umbilical artery”)
    • Pregnancy-induced hypertension in the current or a prior pregnancy
    • Suspicious cardiotocography (CTG)
    • Suspected fetal deformities or diseases
    • Assessing for fetal anemia and hypoxia
    • Growth discordance in multiple pregnancies

References:^[12]