Last updated: November 28, 2023

Summarytoggle arrow icon

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.”

Definitionstoggle arrow icon

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
  • Trimesters of pregnancy
    • First trimester (weeks 1–13)
    • Second trimester (weeks 14–27)
    • Third trimester (weeks 28–40)

Recording systems

Overview of recording systems
Recording system Description Example
TPAL Obstetric recording system that comprises: term births (T), premature births (P), abortions (A), and living children (L) A woman who reports 5 pregnancies with two miscarriages at weeks 11 and 14 of pregnancy, one medical abortion, one delivery at week 39 of pregnancy of a child weighing 3100 g, one delivery at week 29 of pregnancy of a child weighing 2100 g who died soon after birth should be reported as: T1, P1, A3, L1.
GTPAL An extension of the TPAL recording system that also includes gravidity (G) A woman who reports 5 pregnancies with two miscarriages at weeks 11 and 14 of pregnancy, one medical abortion, one delivery at week 39 of pregnancy of a child weighing 3100 g, one delivery at week 29 of pregnancy of a child weighing 2100 g who died soon after birth should be reported as: G5, T1, P1, A3, L1.
GP Obstetric recording system that comprises: gravidities (G) and parities (P) A woman who reports 4 pregnancies and one delivery of an infant weighing 2100 g at week 32 of pregnancy is reported as: G4, P1.

Clinical signs of early pregnancytoggle arrow icon

Presumptive signs

Probable signs [3][4]

Signs Physical findings Weeks of pregnancy
Goodell Cervical softening First 4 weeks
Hegar Softening of the lower segment of the uterus Between 6–8 weeks
Ladin Softening of the midline of the uterus First 6 weeks
Chadwick Bluish discoloration of vagina and cervix Between 6–8 weeks
Telangiectasias and palmar erythema Small blood vessels and redness of the palms First 4 weeks
Chloasma Hyperpigmentation of the face (forehead, cheeks, nose) First 16 weeks

Diagnosis of pregnancytoggle arrow icon

See also “Prenatal care.”

Approach [5]

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

Types of pregnancy tests

Overview of urine and serum hCG tests [17][18]
Urine hCG test Serum hCG test
Test description
  • Qualitative test (less sensitive than quantitative serum pregnancy test)
  • May be a quantitative test (high sensitivity) or qualitative test [13]

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

Interpretation and further investigation of abnormal pregnancy test results
Causes Next steps
Low serum hCG [22]
High serum hCG [28]
Suspected false positive (rare) [18][21][32]
Suspected false negative [18]

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]

Physiological changes during pregnancytoggle arrow icon

Cardiovascular system [35][36]

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]

Renal system [36][38]

Endocrine system [36][39][40]

Hematologic system [36][41][42]

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

Gastrointestinal system [36]

Musculoskeletal system [36]


Reproductive system

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Referencestoggle arrow icon

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