Written and peer-reviewed by physicians—but use at your own risk. Read our disclaimer.

banner image

amboss

Trusted medical answers—in seconds.

Get access to 1,000+ medical articles with instant search
and clinical tools.

Try free for 5 days

Pregnancy

Last updated: March 8, 2021

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 on average lasts 40 weeks. Presumptive signs of pregnancy include amenorrhea, nausea and vomiting, and breast enlargement and tenderness. Preconception counseling assists in the planning of pregnancy through education and risk assessment to help ensure best possible outcomes. Pregnancy can be confirmed definitively via positive serum or urine hCG tests and detection of the embryo on ultrasound. Ultrasound is also used to determine the gestational age and date of delivery. 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). Regular check-ups should be performed to detect potential high-risk pregnancies as well as fetal and maternal complications.

See also “Prenatal care” 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 reached beyond 20 weeks' gestation or terminated with the birth of an infant weighing > 500 g
    • Nulliparity: absence of pregnancies that reached beyond 20 weeks' gestation or birth of an infant weighing > 500 g
    • Primiparity: a history of one pregnancy that reached beyond 20 weeks' gestation or birth of an infant weighing > 500 g
    • Multiparity: a history of more than one pregnancy that reached beyond 20 weeks' gestation or birth of an infant weighing > 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)
    • Periviable birth: live birth occurring between 20–25 weeks of pregnancy
    • Preterm birth: live birth before the completion of 37 weeks (< 37 0/7) of pregnancy
    • Postterm birth: live birth after 42 weeks (> 42 0/7) of pregnancy
  • Trimesters of pregnancy
    • First trimester (weeks 1–13)
    • Second trimester (weeks 14–26)
    • Third trimester (weeks 27–40)

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.

Trimesters of pregnancy

  • First trimester (week 1–13)
  • Second trimester (week 14–26)
  • Third trimester (week 27–40)

Stages of pregnancy

Day/week Stage Possible disorders
Day 0
  • Capacitation: maturation of the sperm in the female genital tract
  • Fertilization (conception): usually occurs in the upper end of the fallopian tubes (most commonly in the ampulla) within 1 day of ovulation
  • Conjugation: fusion of the sperm and ovum to form the zygote (single cell)
Day 1–5
Day 6
Days 6–14
Week 3
  • Embryopathies: complex anomalies of individual organs during a time when the developing embryo is particularly susceptible to teratogens
  • Etiology
    • Infections
    • Drug toxicity
Weeks 3–8
From week 9
  • Fetogenesis: the fetus matures and grows.

The earlier disruptions take place during fetal development, the more complicated the resulting congenital anomalies!

References:[3][4]

General principles

  • Fertile women of reproductive age should be asked about their intention to become pregnant by their healthcare provider (all those planning to become pregnant should receive counseling).
  • Preconception counseling aims to:
    • Identify and address any modifiable factors that may negatively affect pregnancy and childbirth.
    • Educate women and men about options for risk reduction and elimination.

Patient medical history

Lifestyle modifications

  • Recommend maintaining a normal body weight prior to conception.
  • Encourage regular moderate-intensity exercise.
  • Nutrition
  • Substance use
    • Screen all women for alcohol, tobacco, and recreational drug use.
    • Educate about associated adverse effects of substance use on maternal and fetal pregnancy outcomes.
    • Provide assistance and/or refer to the proper specialists for tobacco, alcohol, and recreational drug use cessation.

Management of exposures [7][8]

  • Exposure to harmful agents
    • Advise patients to assess workplace and household for potentially harmful agents (e.g., heavy metals, solvents, chemicals).
    • Educate the patient about the avoidance of harmful agents and refer them to occupational medicine programs as needed.
  • Exposure to violence
    • Screen for family violence at each visit.
    • If ongoing abuse is identified, providers should:
      • Provide community resources to the patient
      • Report the case as appropriate
Probable signs [9][10]
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

Human chorionic gonadotropin (hCG)

β-hCG findings

Description
Normal
Low
High
False-positive

Ultrasound findings in normal pregnancy (abdominal or transvaginal)

  • Confirms pregnancy
  • At 5–6 weeks of pregnancy: detection of the embryo and cardiac activity
  • At 10–12 weeks of pregnancy: detection of fetal heartbeat with doppler ultrasound
  • At 18–20 weeks of pregnancy: fetal movements
Transvaginal ultrasound findings
in normal pregnancy

Ultrasound findings

Gestational age [11][12] β-hCG mlU/mL
Gestational sac 5 1500–2000
Yolk sac 5 2500
Fetal pole 7 5000
Fetal heartbeat 10 17000

Gestational age and estimated date of delivery

  • Naegele rule: used to calculate the date of delivery (due date)
  • Ultrasonography
    • More accurate than Naegele rule
    • Measurement of the crown-rump length (CRL) in the first trimester
    • Measurement of biparietal diameter , fetal femoral length, and abdominal circumference in the second and third trimesters (can be used for determining gestational age starting at 13 weeks) [13]
  • Symphysis fundal height: the length from the top of the uterus to the top of the pubic symphysis
    • Used to assess fetal growth and development from approx. 20 weeks' gestation onwards
    • Development is approx. 1 cm/week after 20 weeks
    • Correlates with gestational age

Cardiovascular system [14][15]

Respiratory system [15][16]

Renal system [15]

Endocrine system [15][17][18]

Hematologic system [15][19][20]

Gastrointestinal system [15]

Musculoskeletal system [15]

Skin

Reproductive system

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

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

Basic principles

  • Nutritional intake: must be adapted to meet the demands of both the mother and the fetus
  • Dietary recommendations
    • Limit caffeine intake: daily recommended dose < 200 mg (this equals about 1–2 cups of coffee or 2–4 cups of caffeinated tea)
    • Avoid alcohol and tobacco use throughout pregnancy. [22]
    • Avoid unwashed or uncooked foods.
    • Avoid fish with possibly high levels of methylmercury, esp. tilefish, swordfish, shark, mackerel, and tuna.
Recommended vitamin and mineral supplementation in pregnancy [23][24]
Supplementation Reason for increased demand Consequences of deficiency
Folic acid [25]
  • Folic acid 0.4–0.8 mg/day
  • Ideally, women should begin intake 4 weeks prior to pregnancy and continue with this dose for at least the first 2–3 months of pregnancy.
Vitamin B12
  • 2.6 mcg/day
  • Recommended for pregnant women who follow a vegan diet.
Iron [28]
  • 30–60 mg/day
Calcium [29][30]
  • 1,000–1,300 mg/day
  • Increased fetal demand (e.g., for bone development)
  • Lactation
Iodine [32]
  • 250 μg/day
  • Increased metabolism and excretion

Recommended weight-gain during pregnancy [33]

  • Recommended weight-gain is determined by BMI prior to pregnancy
    • BMI < 18.5 (underweight): 28–40 lb (12–18 kg)
    • BMI 18.5–24.9 (normal weight): 25–35 lb (11–16 kg)
    • BMI 25–29.9 (overweight): 15–25 lb (7–11 kg)
    • BMI ≥ 30 (obese): 11–20 lb (5–9 kg)
  • Average recommended daily calorie intake
  • Regular physical activity is recommended (see below).
  • Regular physical activity (e.g., aerobic and strength-training exercise) is considered beneficial and is recommended before, during, and after pregnancy.
    • Careful evaluation of medical and obstetric disorders is necessary before recommending regular physical activity.
    • Exercise routines that are considered unsafe during pregnancy should be avoided or modified accordingly.
Safe and unsafe sports during pregnancy [34]
Safe activities
  • High impact training
    • Running, jogging
    • Racquet sports
    • Strength training
  • Low impact training
    • Swimming
    • Walking
    • Stationary cycling
    • Pilates
    • Yoga

Unsafe activities

  • Contact sports (e.g., soccer, basketball)
  • Activities associated with a high risk of falling (e.g., snow and water skiing, gymnastics, surfing)
  • Activities associated with high risk of dehydration (e.g., hot yoga, hot pilates)
  • Extreme sports (e.g., skydiving, scuba diving)

Physical activity should be discontinued in the event of the following: antepartum or postpartum hemorrhage, uterine contractions, amniotic fluid leakage, chest pain, dyspnea before exertion, dizziness, headaches, calf pain/swelling, and/or muscle weakness with impaired balance.

Early identification of high-risk pregnancies is vital in order to prevent the occurrence of maternal and fetal complications. They require regular prenatal care to monitor and support the pregnant mother (see “Prenatal care”).

Risk factors for a complicated pregnancy [35][36]

Oligohydramnios [37]

Potter babies cannot Pee.

POTTER sequence: Pulmonary hypoplasia (lethal), Oligohydramnios (origin), Twisted facies, Twisted skin, Extremity deformities, and Renal agenesis (classic form).

Polyhydramnios [39]

Other complications

Interested in the newest medical research, distilled down to just one minute? Sign up for the One-Minute Telegram in “Tips and links” below.

  1. Anthony J, Osman A, Sani M. Valvular heart disease in pregnancy. Cardiovasc J Afr. 2016; 27 (2): p.111-118. doi: 10.5830/cvja-2016-052 . | Open in Read by QxMD
  2. Soma-Pillay P, Nelson-Piercy C, Tolppanen H, Mebazaa A. Physiological changes in pregnancy. Cardiovasc J Afr. 2016; 27 (2): p.89-94. doi: 10.5830/cvja-2016-021 . | Open in Read by QxMD
  3. LoMauro A, Aliverti A. Respiratory physiology of pregnancy. Breathe. 2015; 11 (4): p.297-301. doi: 10.1183/20734735.008615 . | Open in Read by QxMD
  4. Magon N, Kumar P. Hormones in pregnancy. Nigerian Medical Journal. 2012; 53 (4): p.179. doi: 10.4103/0300-1652.107549 . | Open in Read by QxMD
  5. Cignini P, Cafà EV, Giorlandino C, Capriglione S, Spata A, Dugo N. Thyroid physiology and common diseases in pregnancy: review of literature.. Journal of prenatal medicine. 2012; 6 (4): p.64-71.
  6. Chandra S, Tripathi AK, Mishra S, Amzarul M, Vaish AK. Physiological Changes in Hematological Parameters During Pregnancy. Indian Journal of Hematology and Blood Transfusion. 2012; 28 (3): p.144-146. doi: 10.1007/s12288-012-0175-6 . | Open in Read by QxMD
  7. Bremme KA. Haemostatic changes in pregnancy.. Best Pract Res Clin Haematol. 2003; 16 (2): p.153-168.
  8. Reese JA, Peck JD, Deschamps DR, et al. Platelet Counts during Pregnancy. N Engl J Med. 2018; 379 (1): p.32-43. doi: 10.1056/nejmoa1802897 . | Open in Read by QxMD
  9. Tunzy, Gray. Common Skin Conditions During Pregnancy. American Family Physician. 2007 .
  10. Probable signs of pregnancy. https://brooksidepress.org/ob_newborn_care_1/?page_id=288&cn-reloaded=1. Updated: July 30, 2016. Accessed: September 2, 2020.
  11. Tezuka et al.. Embryonic Heart Rates: Development in Early First Trimester and Clinical Evaluation. Gynecol Obstet Invest. 1991; 32 (4): p.210-212. doi: 10.1159/000293033 . | Open in Read by QxMD
  12. Obstetric Ultrasound. http://www.ob-ultrasound.net/. . Accessed: June 6, 2019.
  13. ISUOG. ISUOG Practice Guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound in Obstetrics & Gynecology. 2012; 41 (1): p.102-113. doi: 10.1002/uog.12342 . | Open in Read by QxMD
  14. Hart TD, Harris MB. Preeclampsia revisited. US Pharm. 2012; 37 (9): p.48-53.
  15. American College of Obstetricians and Gynecologists.. ACOG Committee Opinion No. 764.Medically indicated late-preterm and early-term deliveries.. American Journal of Obstetrics and Gynecology.. 2019 .
  16. Dubil EA, Magann EF. Amniotic fluid as a vital sign for fetal wellbeing. Australasian Journal of Ultrasound in Medicine. 2013; 16 (2): p.62-70. doi: 10.1002/j.2205-0140.2013.tb00167.x . | Open in Read by QxMD
  17. Mousavi AS, Hashemi N, Kashanian M, Sheikhansari N, Bordbar A, Parashi S. Comparison between maternal and neonatal outcome of PPROM in the cases of amniotic fluid index (AFI) of more and less than 5 cm. J Obstet Gynaecol (Lahore). 2018; 38 (5): p.611-615. doi: 10.1080/01443615.2017.1394280 . | Open in Read by QxMD
  18. Salhan S. Textbook of Obstetrics. JP Medical Ltd ; 2016
  19. Taskin S, Pabuccu EG, Kanmaz AG, Kahraman K, Kurtay G. Perinatal outcomes of idiopathic polyhydramnios. Interventional Medicine and Applied Science. 2013; 5 (1): p.21-25. doi: 10.1556/imas.5.2013.1.4 . | Open in Read by QxMD
  20. Sahni M, Ohri A. Meningomyelocele. StatPearls. 2020 .
  21. Hamza A, Herr D, Solomayer E, Meyberg-Solomayer G. Polyhydramnios: Causes, Diagnosis and Therapy. Geburtshilfe Frauenheilkd. 2013; 73 (12): p.1241-1246. doi: 10.1055/s-0033-1360163 . | Open in Read by QxMD
  22. Committee on Obstetric Practice. ACOG Committee Opinion No. 650: Physical Activity and Exercise During Pregnancy and the Postpartum Period. ACOG Comm Opin. 2015 . doi: 10.1097/AOG.0000000000001214 . | Open in Read by QxMD
  23. Le T, Bhushan V, Vasan N. First Aid Step 1. McGraw-Hill Medical; 20th Revised edition edition (2009) ; 2009 : p. 176
  24. Le T, Bhushan V,‎ Sochat M, Chavda Y, Zureick A. First Aid for the USMLE Step 1 2018. McGraw-Hill Medical ; 2017
  25. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017; 27 (3): p.315-389. doi: 10.1089/thy.2016.0457 . | Open in Read by QxMD
  26. American Diabetes Association. 14. Management of Diabetes in Pregnancy: Standards of Medical Care in Diabetes—2019. Diabetes Care. 2018; 42 (Supplement 1): p.S165-S172. doi: 10.2337/dc19-s014 . | Open in Read by QxMD
  27. Farahi N, Zolotor A. Recommendations for preconception counseling and care.. Am Fam Physician. 2013; 88 (8): p.499-506.
  28. ACOG. ACOG Committee Opinion No. 762. Obstetrics & Gynecology. 2019; 133 (1): p.e78-e89. doi: 10.1097/aog.0000000000003013 . | Open in Read by QxMD
  29. Alcohol use in pregnancy. https://www.cdc.gov/ncbddd/fasd/alcohol-use.html. Updated: April 30, 2020. Accessed: August 28, 2020.
  30. Dietary guidelines for Americans 2015-2020. https://health.gov/sites/default/files/2019-09/2015-2020_Dietary_Guidelines.pdf. Updated: December 1, 2015. Accessed: August 28, 2020.
  31. Soneji S, Beltrán-Sánchez H. Association of Special Supplemental Nutrition Program for Women, Infants, and Children With Preterm Birth and Infant Mortality. JAMA Network Open. 2019; 2 (12): p.e1916722. doi: 10.1001/jamanetworkopen.2019.16722 . | Open in Read by QxMD
  32. Bibbins-Domingo et al.. Folic Acid Supplementation for the Prevention of Neural Tube Defects. JAMA. 2017; 317 (2): p.183-189. doi: 10.1001/jama.2016.19438 . | Open in Read by QxMD
  33. Viswanathan M, Treiman KA, Kish-Doto J, Middleton JC, Coker-Schwimmer EJ, Nicholson WK. Folic Acid Supplementation for the Prevention of Neural Tube Defects: An Updated Evidence Report and Systematic Review for the US Preventive Services Task Force.. JAMA. 2017; 317 (2): p.190-203. doi: 10.1001/jama.2016.19193 . | Open in Read by QxMD
  34. McNulty B, McNulty H, Marshall B, et al. Impact of continuing folic acid after the first trimester of pregnancy: findings of a randomized trial of Folic Acid Supplementation in the Second and Third Trimesters.. Am J Clin Nutr. 2013; 98 (1): p.92-8. doi: 10.3945/ajcn.112.057489 . | Open in Read by QxMD
  35. Cantor et al.. Routine Iron Supplementation and Screening for Iron Deficiency Anemia in Pregnancy: A Systematic Review for the U.S. Preventive Services Task Force. Ann Intern Med. 2015; 162 (8): p.566. doi: 10.7326/m14-2932 . | Open in Read by QxMD
  36. Calcium. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/. . Accessed: June 6, 2019.
  37. Mahadevan S, Kumaravel V, Bharath R. Calcium and bone disorders in pregnancy. Indian J Endocrinol Metab. 2012; 16 (3): p.358–363. doi: 10.4103/2230-8210.95665 . | Open in Read by QxMD
  38. Calcium and bone disorders in pregnancy..
  39. Stagnaro-Green A et al. Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid. 2011; 21 (10): p.1081-1125. doi: 10.1089/thy.2011.0087 . | Open in Read by QxMD
  40. Weight gain during pregnancy. https://www.cdc.gov/reproductivehealth/maternalinfanthealth/pregnancy-weight-gain.htm. Updated: January 17, 2019. Accessed: August 28, 2020.
  41. Obstetrics Data Definitions. https://www.acog.org/practice-management/health-it-and-clinical-informatics/revitalize-obstetrics-data-definitions. Updated: January 1, 2014. Accessed: August 27, 2020.
  42. Spong CY. Defining “Term” Pregnancy. JAMA. 2013; 309 (23): p.2445. doi: 10.1001/jama.2013.6235 . | Open in Read by QxMD
  43. Ferri FF. Ferri's Clinical Advisor 2017. Elsevier ; 2016 : p. 1345-1346
  44. Callahan TL, Caughey AB. Blueprints Obstetrics and Gynecology. Lippincott Williams&Wilki ; 2013
  45. Medical Embryology, the Placenta: Decidual Formation.
  46. Smith JA, Refuerzo JS, Ramin SM, Lockwood CJ, Barss VA. Treatment and Outcome of Nausea and Vomiting of Pregnancy. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/treatment-and-outcome-of-nausea-and-vomiting-of-pregnancy.Last updated: January 3, 2017. Accessed: June 16, 2017.
  47. Ehsanipoor RM, Satin AJ, Lockwood CJ, Barss VA. Normal and Abnormal Labor Progression. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/normal-and-abnormal-labor-progression.Last updated: June 7, 2017. Accessed: June 16, 2017.
  48. Refuerzo JS, Smith JA, Ramin SM, Lockwood CL, Barss VA. Clinical Features and Evaluation of Nausea and Vomiting of Pregnancy. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/clinical-features-and-evaluation-of-nausea-and-vomiting-of-pregnancy.Last updated: January 3, 2017. Accessed: July 7, 2017.
  49. American College of Obstetricians and Gynecologists. Practice Bulletin No. 142: Cerclage for the Management of Cervical Insufficiency. Obstet Gynecol. 2014; 123 (2): p.372-379. doi: 10.1097/01.AOG.0000443276.68274.cc . | Open in Read by QxMD
  50. Ressel GW. ACOG Releases Bulletin on Managing Cervical Insufficiency. Am Fam Physician. 2004; 69 (2): p.436-439.
  51. Norwitz ER, Saade GA, Miller HS, Davidson CM. Obstetric Clinical Algorithms. Wiley-Blackwell ; 2016
  52. Berghella V, Lockwood CJ, Barss VA. Cervical Insufficiency. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/cervical-insufficiency.Last updated: January 4, 2017. Accessed: July 7, 2017.
  53. Tao Le, Vikas Bhushan, Deol M, Reyes G. First Aid for the USMLE Step 2 CK, Tenth Edition. McGraw-Hill Education ; 2018
  54. Ciobanu et al.. Thrombocytopenia in Pregnancy.. Maedica. 2016; 11 (1): p.55-60.
  55. Valenti O, Di Prima FA, Renda E, et al. Fetal cardiac function during the first trimester of pregnancy.. Journal of prenatal medicine. 2011; 5 (3): p.59-62.