Pregnancy

Pregnancy begins with the fertilization of the ovum and its subsequent implantation into the uterine wall. The duration of pregnancy is counted in weeks of gestation from the first day of the last menstrual period and is on average 40 weeks. Presumptive signs of pregnancy include amenorrhea, nausea and vomiting, and breast enlargement and tenderness. Pregnancy can be confirmed via positive serum or urine hCG testing. Ultrasound should be obtained to assess pregnancy location and viability in patients if there is concern for ectopic pregnancy or early pregnancy loss, and to determine gestational age and estimated date of delivery if the last menstrual period is not known. Women experience several physiological changes during pregnancy (e.g., increased plasma volume, venous stasis, increased insulin secretion, increased oxygen demand), which can lead to symptoms and conditions that may require treatment (e.g., peripheral edema, insulin resistance, hypercoagulability, dyspnea).

See also “Prenatal care,” “Immunizations in pregnancy,” and “Maternal complications during pregnancy.”

Gravidity, parity, and duration of pregnancy ^[1]

• Gravidity: the number of times a woman has been pregnant, regardless of pregnancy outcome
  • Nulligravidity: no history of pregnancy
  • Primigravidity: history of one pregnancy
  • Multigravidity: history of two or more pregnancies
• Parity: the number of pregnancies that a woman carries beyond 20 weeks of gestation and ends with the birth of an infant weighing > 500 g
  • Nulliparity: no history of a completed pregnancy that reached beyond 20 weeks' gestation or ended with a birth weight of > 500 g
  • Primiparity: a history of one completed pregnancy that reached beyond 20 weeks' gestation or ended with a birth weight of > 500 g
  • Multiparity: a history of more than one pregnancy that reached beyond 20 weeks' gestation or ended with a birth weight of > 500 g
• Fetal age ^[2]
  • Counted as completed weeks of gestation and completed days (0–6) of the current week of pregnancy
  • Gestational age: estimated fetal age (in weeks and days) calculated from the first day of the last menstrual period
  • Conceptional age: the age (in weeks and days) of the fetus calculated from the day of conception (fertilization)
• Duration of pregnancy
  • Normal duration of pregnancy: 40 weeks (280 days)
  • Late-term pregnancy: a pregnancy between 41 0/7 and 41 6/7 weeks' gestation
  • Postterm pregnancy: a pregnancy that extends beyond ≥ 42 0/7 weeks' gestation
• Gestational age at birth
  • Periviable birth: live birth occurring between 20–25 weeks' gestation
  • Preterm birth: live birth before the completion of 37 weeks of gestation (< 37 0/7 weeks' gestation)
  • Postterm birth: live birth after the completion of 42 weeks of gestation (≥ 42 0/7 weeks' gestation)
• Trimesters of pregnancy
  • First trimester (weeks 1–13)
  • Second trimester (weeks 14–27)
  • Third trimester (weeks 28–40)

Recording systems

Presumptive signs

• Amenorrhea
• Nausea and vomiting
• Breast enlargement and tenderness
• Linea nigra: darkening of the midline skin of the abdomen
• Hyperpigmentation of the areola
• Abdominal bloating and constipation
• Increased weight gain
• Cravings for or aversions to certain foods
• Increased urinary frequency
• Fatigue

Probable signs ^[3][4]

See also “Prenatal care.”

Approach ^[5]

• Confirm pregnancy by measuring human chorionic gonadotropin (hCG) in urine and/or serum. ^[6]
• If there is concern for ectopic pregnancy or early pregnancy loss: ^[7][8]
  • Obtain ultrasound to confirm a viable intrauterine pregnancy (IUP).
  • Monitor with serial ultrasound and/or serum hCG until pregnancy viability and location are confirmed. ^[9][10]
• Determine gestational age and estimated date of delivery using the date of the last menstrual period and/or ultrasound. ^[11]
• Refer for follow-up care depending on desire for continuation of pregnancy: ^[6][12]
  • Prenatal care, if continuation of pregnancy is desired
  • Induced abortion, if termination is desired

Early identification of pregnancy with accurate dating is important for routine pregnancy monitoring (e.g., timing screening tests) and for assessment of potential pregnancy complications (e.g., identification of preterm labor and postterm pregnancy). ^[5]

Pregnancy test

hCG physiology

• Pregnancy tests detect the presence of human chorionic gonadotropin (hCG) in blood or urine.
• hCG is produced during pregnancy, primarily by the placental syncytiotrophoblast. ^[13][14]
• The role of hCG is to: ^[13][14][15]
  • Stimulate progesterone secretion by the corpus luteum during the first 3–6 weeks of gestation to maintain pregnancy ^[13][14]
    • Prior to pregnancy, LH stimulates corpus luteal progesterone secretion. ^[16]
    • After the luteal placental shift, the placenta produces progesterone. ^[13][16]
  • Promote uterine angiogenesis
  • Promote myometrial stability, preventing contractions prior to labor
  • Support immune tolerance to the growing embryo ^[14]
• Structure
  • α-subunit: common to hCG, FSH, LH, and TSH ^[13]
  • β-subunit
    • Specific to hCG ^[13][14]
    • Pregnancy tests generally detect hCG through antibodies to the β-subunit. ^[15]

Types of pregnancy tests

Interpretation ^[10][24]

Expected findings during pregnancy ^[10]

• Doubling of hCG every 1.8–3 days for the first 6–7 weeks of pregnancy ^[20]
• Peak hCG at 8–12 weeks of gestation (peak value ∼ 100,000 mlU/mL) ^[22][24]
• Decrease in hCG during the second trimester ^[24]
• Steady hCG level during the third trimester ^[13]

Abnormal hCG results

Ultrasound confirmation of normal intrauterine pregnancy ^[34]

For detailed information on ultrasound indications and techniques in pregnancy, see “Ultrasound during pregnancy” and “POCUS in early pregnancy.”

• 4–5 weeks' gestation: : gestational sac generally visible with transvaginal ultrasound when serum hCG levels reach 1500–3000 mIU/mL ^[9]
• 5–6 weeks' gestation: detection of the yolk sac
• 6–7 weeks' gestation: detection of the fetal pole (embryo) and cardiac activity with transvaginal ultrasound ^[34]
• 7–8 weeks' gestation: Physical features can be visualized (e.g., spine, limb buds, early head structure).
• > 8 weeks' gestation: embryo/fetal movement
• 10–12 weeks' gestation: detection of fetal heartbeat with motion-mode (M-mode) scanning or video archiving ^[11]

The presence of a gestational sac containing either a yolk sac, fetus, or embryo, with or without cardiac activity, in the uterus suffices to confirm an intrauterine pregnancy. ^[8]

Cardiovascular system ^[35][36]

• ↑ Progesterone → ↓ vascular tone → ↓ peripheral vascular resistance (↓ afterload)
  • ↑ Cardiac output by up to 40% (↑ preload)
  • ↑ Stroke volume (by 10–30%)
  • ↑ Heart rate (by ∼ 12–18 bpm) → ↑ uterine perfusion
  • ↓ Mean arterial pressure
• Innocent systolic murmur
• The apex beat is displaced upward.
• ↑ Plasma volume → ↓ oncotic pressure → edema of lower limbs
• Varicosities
• Aggravation of preexisting valvular diseases

The gravid uterus can compress the inferior vena cava and pelvic veins thereby decreasing venous return.

A physiological systolic murmur may be heard due to increased cardiac output and increased plasma volume.

Respiratory system ^[37]

• ↑ Oxygen consumption (by approx. 20%)
• ↑ Intraabdominal pressure through uterine growth → dyspnea (the diaphragm is displaced upwards → ↓ total lung capacity, residual volume, functional residual capacity, and expiratory reserve volume)
• Progesterone stimulates the respiratory centers in the brain → hyperventilation (to eliminate fetal CO₂ more efficiently) → physiological, chronic compensated respiratory alkalosis
  • ↑ Tidal volume → ↑ minute ventilation
  • ↓ PCO₂ (∼ 30 mm Hg)

Renal system ^[36][38]

• ↑ Renal plasma flow ; → ↑ GFR → ↓ BUN and creatinine
• ↑ Aldosterone → ↑ plasma volume and hypernatremia
• ↑ Progesterone and intraabdominal pressure → dilation of kidney, pelvis, and calyceal systems → reduced tone and peristalsis
  • Hydronephrosis and hydroureter
  • Hypomotility of the ureters → urinary stasis → pyelonephritis
• ↑ Urinary frequency
• ↑ Glucose levels in urine: Increased glomerular filtration results in overload of the glucose carrier responsible for its resorption.
• Mild proteinuria: Increased GFR and glomerular permeability to albumin increases protein excretion.

Endocrine system ^[36][39][40]

• Progesterone
  • Responsible for pregnancy maintenance
  • Produced by the corpus luteum until the 10–12 weeks of gestation, after which it is produced by the fetoplacental unit
• Human placental lactogen: a hormone synthesized by syncytiotrophoblasts of the placenta, which promotes the production of insulin-like growth factors.
  • Increases insulin levels
  • Causes insulin resistance
  • Increases serum glucose levels and lipolysis to ensure sufficient glucose supply for the fetus
  • Maternal insulin resistance begins in the second trimester and peaks in the third trimester.
• Thyroid hormones
  • ↑ hCG → ↓ TSH levels during the first part of the first trimester
  • ↑ TBG → ↑ T₄ and T₃ → slightly increased free T₄ and T₃ levels during first trimester
  • Free T4 and T3 levels decrease during the second and third trimesters
• ↑ SHBG and corticosteroid-binding globulin
• ↑ Triglycerides and cholesterol (due to increased lipolysis and fat utilization)
• Hyperplasia of lactotroph cells in the anterior pituitary → physiological enlargement of the pituitary gland (up to 40% increase from pregestational volume)

Hematologic system ^[36][41][42]

• ↑ Plasma volume → ↓ hematocrit, especially towards the end of pregnancy (30–34^th week of gestation) → dilutional anemia (hemoglobin value rarely drops below 11 g/dL)
• Hypercoagulability is due to an increase in fibrinogen, factor VII, and factor VIII and a decrease in protein S; (reduces the risk of intrapartum blood loss).
• ↓ Platelet count → gestational thrombocytopenia
• ↑ RBC mass (increases from 8–10^th week of gestation until the end of pregnancy)
• ↓ Iron and folate levels due to increased vitamin and mineral requirements
• ↑ WBC count
• ↓ Albumin
• ↑ Alkaline phosphatase (placental isoenzymes)

Physiological hypercoagulability during pregnancy leads to an increased risk of thrombosis. Patients with thrombophilia should receive adequate thrombosis prophylaxis.

Gastrointestinal system ^[36]

• ↑ Salivation
• ↓ Lower esophageal sphincter tone → gastroesophageal reflux
• ↓ Motility → constipation and bloating
• Gallbladder stasis → gallstones
• Hemorrhoids

Musculoskeletal system ^[36]

• ↑ Body weight → forward shift in center of gravity → ↑ lumbar lordosis
• ↑ Intraabdominal pressure → diastasis recti; meralgia paresthetica
• Relaxation of the pelvic girdle ligaments and symphysis pubis; → pelvic girdle pain, coccygeal pain
• Fluid retention in tissue → carpal tunnel syndrome

Skin

• Spider angioma
• Palmar erythema
• Striae gravidarum: scarring that manifests as erythematous, violaceous, and/or hypopigmented linear striations on the abdomen
• Hyperpigmentation: chloasma, linea nigra, hyperpigmentation of the nipples

Reproductive system

• Uterus: increase in size
• Vulva and vagina
  • Vaginal discharge
  • Formation of varicose veins
• Mammary glands: increase in size; breast fullness and tenderness

• One-Minute Telegram 9-2020-2/3: COVID-19: Pregnant women at increased risk for complications

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