Pregnancy: Diagnosis, Maternal Physiology, and Routine Care

Diagnosis of Pregnancy and Establishing the EDD

Pregnancy is confirmed based on lab tests and obstetric ultrasound imaging. 

Laboratory

The major analyte used to establish pregnancy is β-hCG. 

• β-hCG is a hormone produced early by the developing embryo.
• The presence of β-hCG indicates pregnancy.
• β-hCG tests may be:
  • Qualitative: to detect the presence or absence of β-hCG
    • Urine tests (available as over-the-counter kits) or a test at a medical lab
    • Reliable approximately 2 weeks after fertilization
  • Quantitative: to determine serum β-hCG levels
    • Serum tests
    • More sensitive, reliable 6–10 days after fertilization 
    • Can be used to track β-hCG levels when there is a concern for an abnormal pregnancy (e.g., ectopic pregnancy or miscarriage)
    • Levels should roughly double every 24–48 hours during the 1st month.

Imaging

• Ultrasound is the obstetric imaging modality of choice to diagnose and date a pregnancy.
• Purpose of early ultrasounds:
  • Viability: to establish if a viable pregnancy is present
  • To determine the number of fetuses
  • To establish the location of the pregnancy (e.g., rule out ectopic pregnancy)
  • Dating
• 1st-trimester findings: 
  • Presence of a gestational sac:
    • 1st visible finding of pregnancy is seen around 4.5–5 wga.
    • A hypoechoic circle within the uterine cavity, surrounded by hyperechoic endometrium
    • Should be visible in the uterus if quantitative serum β-hCG is > 2,000
  • Presence of a yolk sac: 
    • A thin hyperechoic ring within the gestational sac
    • 1st seen approximately 5–6 wga and disappears around 10 wga
  • Presence of a fetal pole with a heartbeat: seen around 5.5–6 wga
• Dating a pregnancy using ultrasound:
  • 1st trimester: measuring the crown-rump length of the fetal pole 
  • 2nd and 3rd trimesters: calculated using a formula by considering measurements of biparietal diameter, abdominal circumference, and femur length

Establishing the EDD

Establishing the EDD is one of the most important factors to accomplish after diagnosing a pregnancy. Dating a pregnancy is usually done by calculating the EDD from the LMP and comparing that date with the EDD obtained from early ultrasound measurements.

• Calculating the EDD from the LMP:
  • The date that falls exactly 40 weeks after the LMP
  • Calculated by adding 280 days (or 9 months and 7 days) to the LMP
• Dating by ultrasound:
  • Measure the crown-rump length and look up the associated date in a table (most ultrasound machines will show this along with the measurement).
  • Ultrasound dating is most accurate in the 1st trimester before genetic variation and the effects of intrauterine environment begin to have greater effects on fetal growth.
• Establishing the final EDD:
  • Use the EDD obtained from the LMP if the EDD obtained from the crown-rump length measurement is within:
    • 5 days of the LMP-EDD for pregnancies < 9 wga
    • 7 days of the LMP-EDD for pregnancies 9–13 + 6 wga
    • Approximately 2 weeks in the 2nd trimester
    • Approximately 3 weeks in the 3rd trimester
  • Use the EDD obtained from ultrasound if the EDDs are further apart from each other than the dates listed above.
• Calculating the EDD from the LMP is the most accurate method to date a pregnancy if that EDD is consistent with the dates obtained from the ultrasound.
• If the LMP is unknown, a 1st-trimester ultrasound is the next most accurate way to date a pregnancy.

Physiological Changes During Pregnancy

To support fetal growth and development and prepare the mother’s body for eventual delivery, numerous anatomic and physiologic changes occur within a woman’s body during pregnancy.

Reproductive tract

Uterus:

• Increased uterine size:
  • Mass ↑ from approximately 70 grams to 1100 grams
  • Volume capacity ↑ from approximately 10 mL to 5 L
  • Hypertrophy of the uterine wall with an accumulation of fibrous and elastic tissue
  • Growth is initiated through ↑ estrogen levels
  • By 28 wga, uterine growth slows and the uterus continues to stretch and become thinner.
• Blood flow: ↑ from 50 mL/min to 450–750 mL/min at term 
• Muscle contraction:
  • Uterus is maintained in a passive noncontractile state through ↑ levels of progesterone (a smooth muscle relaxant)
  • Braxton-Hicks contractions: 
    • Irregular contractions that do not cause cervical change
    • More noticeable as the pregnancy progresses 
• Uterine involution: return of the uterus to its pre-pregnant state in the 1st several weeks postpartum

Cervix:

• Cervix softens and can become bluish due to:
  • Edema
  • Increased vascularization
  • Hypertrophy and hyperplasia of the cervical glands
• May undergo eversion:
  • Glandular cells normally lining the cervical canal become visible on the surface of the cervix.
  • Can cause benign bleeding (all bleeding in pregnancy should be fully worked up)
• Endocervical mucosal cells produce a mucus plug, an immunological barrier for uterine contents.

Ovaries:

• Ovulation and follicle development are suppressed by ↑ estrogen levels
• The corpus luteum supplies progesterone during the 1st part of pregnancy until the placenta is developed enough to take over this function.

Anatomic and physiologic changes in pregnancy by system

Skin changes

• Stretch marks
• Hyperpigmentation of:
  • Face (known as melasma, or the “mask of pregnancy”)
  • Nipples
  • Perineum
  • Abdominal line (known as the linea nigra)
  • Umbilicus
• Spider angiomata
• Palmar erythema

Normal Prenatal Care

Appointment schedule

The typical schedule of prenatal visits for low-risk individuals:

• Every 4 weeks up through 28 wga
• Every 2 weeks from 28–36 wga
• Every week from 36 wga until delivery

Prenatal visits

Parameters to measure/monitor for healthy, uncomplicated individuals at routine prenatal visits:

• 1st visit:
  • Ultrasound to confirm the estimated date of confinement (either in-office or ordered)
  • Full physical exam, including a pelvic exam
  • Recommend supplements: 
    • Folic acid (best if started prior to pregnancy)
    • Multivitamins with iron
• All visits:
  • Weight
  • Blood pressure
  • Fetal HR (using doppler auscultation)
  • Ask the mother about:
    • Abnormal bleeding
    • Contraction-like or cramping abdominal pain
    • Abnormal loss of fluid
• Starting at 20 wga: fundal height measurements
• Starting at 28 wga, ask the mother about: 
  • Fetal movements:
    • Should experience 10 movements in a 2-hour period at least once daily
    • Individuals who report decreased fetal movement should be evaluated.
  • TDaP immunization (once)
  • Rh immunoglobulin to Rh-negative women
• Starting at 34–36 wga: Assess fetal presentation (vertex or breech).

Routine pregnancy laboratory and imaging studies

All pregnant individuals should have certain labs done at different points during their pregnancy. These include:

• At their 1st obstetrics appointment:
  • CBC
  • Blood type and screen (may indicate future compatibility issues with fetal blood type)
  • Urinalysis
  • Rubella immunity status
  • HIV
  • Hepatitis B surface antigen
  • Rapid plasma reagin test for syphilis
  • Gonorrhea and chlamydia testing
  • Pap smear (only if due for routine Pap screening)
  • Screening for inherited diseases based on ethnicity (e.g., hemoglobinopathies, cystic fibrosis)
• Screening for fetal aneuploidy (e.g., trisomy 21):
  • Multiple options available
  • Options include different combinations of multiple serum analytes and ultrasound.
  • A common option used is a test assessing the cell-free fetal DNA found in maternal serum (often referred to as noninvasive prenatal testing (NIPT)).
• Other tests:
  • Full anatomic assessment of the fetus, placenta, and uterus/cervix at 18–22 wga 
  • 1-hour glucose tolerance test (GTT) at 24–28 wga
  • CBC is often repeated with GTT.
  • Group B Streptococcus culture at 35–37 wga
  • Bedside ultrasound to check fetal presentation (vertex/head down, breech/buttocks down) around 35 wga

Diet, exercise, and weight gain

Weight gain:

The recommended weight gain during pregnancy is based on the individual’s prepregnancy BMI. Normal weight-gain recommendations:

• 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.

Exercise:

• 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, women can continue performing exercises they were doing prior to pregnancy at the same level of intensity (goal: maintain fitness level rather than increasing exercise intensity).
• Avoid contact sports and/or activities associated with the risk of falling or abdominal trauma (e.g., soccer, horseback riding, downhill skiing).
• Avoid exercising in hot weather.

Safety

• Air travel is safe for up to 36 weeks (after which, the risk of labor or complications on board ↑).
• Precautions to prevent deep vein thrombosis during long trips (both flights and road trips):
  • Compression stockings
  • Frequent hydration
  • Frequent ambulation in the airplane or at rest stops (every 1–2 hours)
• Frequent handwashing
• Avoid kitty litter (to ↓ risk of toxoplasmosis).