Prenatal Care

Prenatal care is a systematic and periodic assessment of pregnant women during gestation to assure the best health outcome for the mother and her fetus. Prenatal care prevents and identifies maternal and fetal problems that adversely affect the pregnancy outcome. Prenatal visits involve scheduled screening tests such as prenatal ultrasounds or blood glucose tests and measurements of fetal/maternal health metrics. These visits are also opportunities to educate pregnant women about pregnancy, labor, delivery, and parenting while providing psychological support to patients and their families.

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Initial Prenatal Visit


The initial prenatal visit is often the most important. Objectives of this visit include:

  • Pregnancy confirmation 
  • Establishing the gestational age and estimated due date (EDD)
  • A comprehensive medical history and physical exam
  • Routine laboratory assessments
  • Counseling
  • Determine the pregnancy risk and establish the follow-up schedule (based on risk):
    • Low-risk pregnancy:
      • Every 4 weeks until 28 weeks gestational age (wGA)
      • Every 2 weeks from 28 to 36 wGA
      • Weekly from 36 wGA to delivery
    • High-risk pregnancy:
      • Highly individualized
      • Visit frequency varies according to disease and response to treatment.

History and exam

Important areas to cover (and why they are important) include:

Obstetric history:

  • Gravidity and parity
  • Mode of deliveries:
    • E.g., vaginal or cesarean delivery (CD)
    • Certain types of cesarean incisions (ones that include the uterine fundus) carry a high risk of uterine rupture during subsequent labors → these individuals should have a repeat CD
  • Gestational age at prior deliveries:
    • E.g., full-term or preterm delivery
    • History of a prior preterm delivery ↑ risk for preterm delivery in this pregnancy
  • Prior pregnancy, delivery, and/or postpartum complications
    • May ↑ risk for complications in this pregnancy
    • May be indications for additional treatment:
      • Example: Patients with a history of severe preeclampsia can be treated with aspirin to help reduce the risk of preeclampsia in this pregnancy.

Gynecologic history:

  • Age of menarche 
  • Typical menstrual cycles → to help assess accuracy of pregnancy dating using the last menstrual period (LMP)
  • History of genital herpes → patients with genital HSV should: 
    • Receive antiviral prophylaxis with acyclovir starting around 36 wGA
    • Be evaluated specifically for any signs of active lesions (including on the cervix) at the onset of labor
    • Active lesions at the time of labor are a relative contraindication to vaginal delivery.
  • Previous gynecological operations, especially: 
    • Procedures to remove uterine fibroids → women with prior full-thickness incisions in the uterine fundus should not labor due to ↑ risk of uterine rupture
    • Loop electrical excision procedure for abnormal cervical cytology
      • May ↑ risk of a cervical insufficiency/preterm delivery
      • Scar tissue may prevent normal cervical dilation and ↑ risk for CD

Past medical and surgical history:

With the medical history, the physician needs to determine whether the patient has any conditions that alter the course or risks of pregnancy, and make sure any conditions that may be altered by pregnancy are appropriately managed. Common examples of important conditions are:  

  • Diabetes mellitus: requires close management during pregnancy to maintain normal glucose levels and prevent fetal complications
  • Hypothyroidism: Levothyroxine dosing often needs to be adjusted during pregnancy.
  • Hypertension: ↑ risk for pregnancy complications, especially poor fetal growth and superimposed preeclampsia
  • Cardiopulmonary disease: may have ↑ risk with Valsalva during delivery
  • Thrombophilia (e.g., idiopathic thrombocytopenic purpura): may prevent the safe insertion of an epidural catheter during labor
  • Autoimmune disease (e.g., systemic lupus erythematosus): 
    • Pregnancy may cause flares.
    • Verify safety of medications.
  • Non-gynecologic surgeries:
    • For example, if the patient presents with abdominal pain in the right lower quadrant but has a history of an appendectomy, this rules out appendicitis.

Family history:

Family history is important to guide screening for potential inherited conditions in the fetus.

  • Inherited diseases (e.g., thalassemia, cystic fibrosis (CF), sickle cell anemia)
  • Congenital malformations (e.g., cardiac diseases)

Social history:

  • Substance abuse: may have adverse effects on fetal development
    • Smoking
    • Alcohol use
    • Drug abuse
  • Presence or absence of support system 
  • Screening for domestic violence

Medication and allergies:

Medications should be reviewed for:

  • Safety in pregnancy and lactation
  • Dosing adjustments

Physical exam:

A complete physical exam should be performed. Special attention should be paid to:

  • Vital signs
  • Height, weight, and BMI
  • Pelvic exam:
    • Assess adequacy of the bony pelvis (is there enough space for the fetus to pass through during delivery?)
    • Are there any anatomic abnormalities of the vagina, cervix, or perineum that may affect labor and/or delivery (e.g., presence of a vaginal septum)?
  • Heart and lung exam

Pregnancy confirmation

Pregnancy can be confirmed with:

  • A urine hCG test
  • Assessment of the fetal heart rate (FHR) (either by ultrasound if early in the pregnancy or by handheld doppler)

Pregnancy dating

An EDD should be established at every initial prenatal visit. The 2 primary methods to do this are:

  • Estimation using the LMP
  • Ultrasonographic measurements (e.g., crown-rump length)

Typically, a combination of both LMP and ultrasound dating are used to determine the best EDD. Once established, the EDD does not change during the pregnancy.

Ultrasound image of a 12-week fetus

Ultrasound image of a 12-week fetus:
The broken yellow line is the crown-rump length measurement.

Image: “Ultrasound image of a 12-week fetus” by Child Health, Royal Aberdeen Children’s Hospital, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZG, UK. License: CC BY 3.0


Ultrasonography is the imaging modality of choice and the most accurate tool to estimate gestational age early in pregnancy (used in conjunction with the LMP). All pregnant women should have an ultrasound at (or ordered at) the initial visit in order to confirm:

  • Pregnancy and fetal viability
  • Fetus location (intrauterine pregnancy)
  • Most accurate due date
  • Number of fetuses and chorionicity in multiple gestations (e.g., twins)
  • Findings of abnormal uterine and adnexal masses


There are a number of routine laboratory tests that should be ordered at the initial prenatal visit. These include: 

  • CBC
    • Check for current anemia and thrombocytopenia.
    • Obtain baseline hemoglobin and platelet counts (to compare future values to, since anemia and thrombocytopenia are common in pregnancy).
    • Iron deficiency anemia is the most common. 
  • Blood typing and antibody screening
    • Identify ABO blood group and rhesus D factor.
    • If the patient is Rh positive, their cells have the Rh antigen.
    • If the patient is Rh negative, their cells lack the Rh antigen.
      • If they have prior exposure to the Rh antigen (such as from placental bleeding with an Rh-positive infant) → patient may have developed antibodies against Rh factor (known as sensitization)
      • The antibodies produced by a sensitized Rh-negative mother may attack an Rh-positive fetus, resulting in fetal demise if not managed appropriately.
    • The antibody screening is looking for a number of different maternal antibodies that may attack fetal blood cells and potentially cause fetal demise.
  • Rubella and varicella antibody titers
    • Nonimmune individuals are at risk for giving birth to a baby with congenital rubella or varicella syndromes.
    • Rubella and varicella vaccines are contraindicated in pregnancy.
    • Nonimmune women should be counseled to avoid sick people and to be vaccinated after pregnancy.
    • Pregnant women exposed to varicella can be treated with immunoglobulin.
  • Hepatitis B surface antigen (HBsAg) serology screening
    • If HBsAg positive, the newborn should be given the vaccine for hepatitis B virus (HBV) and immunoglobulin upon birth to ↓ risk of vertical transmission
  • HIV test
    • High risk of vertical transmission to the infant in poorly controlled HIV/AIDS
    • Patients should be managed with antiretroviral therapy.
  • Rapid plasma reagin (screening test for syphilis)
    • If the test is positive, syphilis should be confirmed with a VDRL test.
    • Vertical transmission is associated with a high incidence of neonatal mortality and morbidity.
      • Nonimmune hydrops fetalis
      • Intrauterine growth restriction (IUGR) 
      • Skeletal abnormalities
      • Pneumonia
      • CNS symptoms
    • Treat with penicillin.
  • Chlamydia and gonorrhea nucleic acid amplification tests (NAAT) 
    • All pregnant women < 25 years of age should be tested.
    • Test pregnant women > 25 years of age with risk factors for STIs.
    • STIs ↑ risk for:
      • Preterm labor/delivery (infections make the uterus “irritable”)
      • Neonatal infection
  • Urinalysis and urine culture
    • Screen for proteinuria and asymptomatic bacteriuria.
    • Patients are at increased risk for ascending urinary tract infections (UTIs) (e.g., pyelonephritis) in pregnancy.
  • Pap smear
    • Only if indicated by routine screening guidelines
  • TB skin test
    • In high-risk situations, such as close contact with someone infected with TB or if infected with HIV

Initial visit interventions and counseling


  • Initiate folic acid supplementation:
    • Generally at least 400 mcg daily
    • Taken 1 month before and during pregnancy can help prevent neural tube defects
  • Prenatal vitamins: typically include both folic acid and iron to prevent anemia

Warning signs:

Patients should be advised to seek medical attention for:

  • Bleeding
  • Cramping/pelvic pain

Subsequent Prenatal Visits

After the initial prenatal visit, the regular schedule for otherwise healthy pregnant women 18–35 years old should be monthly until 28 wGA, bimonthly from 28–36 wGA, and weekly from 36 wGA until delivery.


At every visit:

  • Maternal weight 
  • Blood pressure
  • Document FHR with auscultation or ultrasound
  • Starting at 20 weeks: fundal height (FH) measurement
    • FH should be approximately equal in centimeters to their gestational age in weeks (+/- 3 cm).
    • FH should continue to grow each visit.
    • Inappropriate FH measurements should prompt further evaluation with an ultrasound to measure:
      • Fetal growth
      • Fluid levels
  • Starting around 28 weeks: fetal movement (FM)
    • Patients should be instructed to do daily fetal kick counts (FKCs).
    • FKCs: should feel at least 10 movements in a 2-hour time period at least once per day
    • Patients who report decreased FM should be evaluated with fetal monitoring.
  • Ask mother about:
    • Abnormal bleeding
    • Contraction-like or cramping abdominal pain
    • Abnormal loss of fluid

Laboratory and imaging assessments and interventions

18‒22 weeks: full anatomic assessment of the fetus, placenta, and uterus/cervix

24–28 weeks:

  • Repeat CBC to look for:
    • Anemia 
    • Thrombocytopenia
  • Glucose tolerance test (GTT):
    • Screening for gestational diabetes mellitus (GDM)
    • A 50 gm 1-hour screening oral glucose tolerance test (OGTT)
    • If the test is abnormal, a 3-hour OGTT should be performed to diagnose or exclude GDM.
  • Rh-negative mothers:
    • Repeat Rh and antibody screening 
    • Administer RhoGam

28‒36 weeks:

  • Tdap vaccine in all patients
  • Rescreen for STDs in high-risk patients.
  • Group B streptococcal (GBS) culture:
    • Obtain an anovaginal culture at 35–37 wGA.
    • Group B streptococci (GBS) are a primary cause of neonatal sepsis.
    • If positive, then intrapartum with a penicillin
  • Bedside ultrasound to assess fetal presentation (vertex/head down, or breech/buttocks down)

Prenatal Screening for Genetic Abnormalities

There are a number of noninvasive tests that are available to assist in prenatal diagnosis of genetic conditions. In some cases, if screening tests are positive, more-invasive prenatal diagnostic techniques are available to provide definite diagnosis. 

Aneuploidy screening tests

  • Multiple options available
  • Options include different combinations of multiple serum analytes and ultrasound, which can include:
    • Ultrasound measurement of the nuchal translucency 
    • Ultrasound assessment of “soft markers” for aneuploidy (findings more common in fetuses with aneuploidy, which adjust the overall risk); examples include:
      • Echogenic intracardiac foci (e.g., calcifications)
      • Short femur length
      • Echogenic bowel
    • 1st-trimester serum analytes:
      • Pregnancy-associated plasma protein A
      • β-hCG
    • 2nd-trimester serum analytes: 
      • β-hCG
      • Unconjugated estriol
      • Maternal alpha-fetoprotein (AFP) level
      • Inhibin A level
  • Cell-free fetal DNA:
    • A screening test analyzing fetal DNA found in maternal serum (a maternal blood test) 
    • Often referred to as noninvasive prenatal screening (NIPS)
    • Performed after 10 wGA
    • 99% accurate
  • Serum-integrated, sequential, or contingency screening:
    • Different combinations of serum analytes tested in both the 1st and potentially 2nd trimester
    • May be combined with nuchal translucency measurements
    • Gives the probability of aneuploidy
    • Detection rate: 95% 
  • Quad screen:
    • 2nd-trimester screening of maternal serum analytes
    • Gives the probability of aneuploidy
    • Detection rate: 81%

Confirmatory diagnostic tests for aneuploidy

If aneuploidy screening tests are abnormal, patients can be referred for more invasive diagnostic testing, which can include:

  • Chorionic villus sampling (CVS):
    • Performed at 10–14 wGA
    • A needle is inserted through the maternal abdomen into the chorionic villi and blood is drawn.
    • Karyotype analysis is performed on the fetal blood cells.
  • Amniocentesis: 
    • Performed around 15 wGA or greater
    • A needle is inserted through the maternal abdomen and amniotic fluid is aspirated.
    • Karyotype analysis is performed on fetal cells present in the amniotic fluid.
  • Risks of invasive testing:
    • Bleeding
    • Infection
    • Fetal loss


Image by Lecturio.

Parental genetic carrier screening tests

Some patients may be at higher risk than others for certain inherited genetic conditions. Based on specific risk factors, typically including family history and race/ethnicity, additional genetic screening can be offered. Most commonly, this includes carrier screening for:

  • Cystic fibrosis (CF)
  • Sickle cell anemia
  • Thalassemias
  • Spinal muscular atrophy
  • Fragile X syndrome
  • Ashkenazi Jewish genetic panel (AJGP), which includes multiple conditions, some of which are:
    • Tay sachs disease
    • Canavan disease
    • Gaucher disease
    • Familial dysautonomia
    • CF
    • Fanconi anemia (FA)


Physicians play an important role in providing women with accurate information on how to stay safe and healthy during pregnancy.


Table: Safe and unsafe diet in pregnancy
  • Moderate caffeine intake
  • Artificial sweeteners
  • Fish: Limit to < 12 oz per week.
  • Excess caffeine intake
  • Saccharine
  • Unpasteurized food, especially dairy (risk of listeria)
  • Swordfish, shark, king mackerel, or raw fish (risk of mercury poisoning)

Weight gain

The amount of recommended weight gain during pregnancy is based on the patient’s prepregnancy BMI. Normal weight gain recommendations are:

  • Underweight (BMI < 18.5): 28–40 lbs 
  • Normal weight (BMI 18.5–24.9) : 25–35 lbs 
  • Overweight (BMI 25–29.9) : 15–25 lbs 
  • Obese (BMI > 30): 11–20 lbs 
  • Note: Weight loss is not recommended during pregnancy. 


  • Purpose: controls weight gain, improves delivery, improves weight loss after pregnancy
  • Recommendation: moderate exercise for 30 minutes on most days of the week
  • In general, patients can continue doing exercises they were doing before pregnancy, at the same level of intensity (goal: maintain fitness level rather than increasing it).
  • Avoid contact sports and/or activities with risk of falling or abdominal trauma (e.g., soccer, horseback riding, downhill skiing).
  • Avoid exercising in hot weather due to ↑ risks associated with dehydration (e.g., preterm labor)


  • Pregnancy hormones (e.g., progesterone, relaxin) cause ligaments to stretch more easily and ↑ water retention
  • Common pains:
    • Pelvic pain from stretching at the pubic symphysis and sacroiliac joints → maternity support belts can help
    • Round ligament pain (see below)
    • Foot pain
    • Low back pain (from shifting center of gravity)
    • Carpal tunnel syndrome (CTS)
  • Round ligament pain: 
    • The round ligaments are ligaments attaching the uterus to the pelvic sidewall.
    • As the uterus grows, these ligaments can stretch and cause pain.
    • Differentiating round ligament pain (benign) from more concerning pain: 
      • Round ligament pain is often unilateral.
      • On exam, push the uterus toward the painful side; if this maneuver relieves the pain, it is likely round ligament pain.
  • Analgesic use:
    • Acetaminophen is the safest analgesic.
    • Try to avoid NSAIDs due to there effects on the fetal kidneys.

GI symptoms

  • Nausea and vomiting:
    • Common, especially in early pregnancy (colloquially, “morning sickness”)
    • More common in the mornings but may occur throughout the day
    • Often improves in the early 2nd trimester
    • Management:
      • Vitamin B6 supplementation
      • Dietary changes: Eat first thing in the morning, and eat smaller, more frequent meals.
  • Acid reflux/heartburn
  • Constipation


  • Air travel is safe up to 36 weeks, after which risk of labor or complications on board ↑
  • Deep vein thrombosis (DVT) precautions for long trips (both flights and car trips):
    • Compression stockings
    • Frequent hydration
    • Frequent ambulation around the plane or at rest stops (every 1–2 hours)
  • Frequent hand-washing
  • Avoid kitty litter (to ↓ risk of toxoplasmosis)


  1. Centers for Disease Control and Prevention. (2015). Preconception health and health.  (2015). Preconception health and health care.  Retrieved June 14, 2021, from
  2. The American College of Obstetricians and Gynecologists. (2020). Routine tests during pregnancy. Retrieved June 14, 2021, from
  3. Lockwood, C, & Magriples, U. (2021). Prenatal care: Initial assessment. In Barss, V.A. (Ed.), UpToDate. Retrieved July 28, 2021 from 

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