- Clinical science
Pregnancy begins with the fertilization of the ovum and 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. 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 benign, physiological changes during pregnancy (e.g., peripheral edema, dyspnea, increased urinary frequency). Regular check-ups should be performed to detect possible high-risk pregnancies as well as fetal and maternal complications.
See also maternal complications during pregnancy.
- The duration of pregnancy is counted in weeks of gestation from the first day of the last menstrual period
- Completed weeks of gestation + completed days (0–6) of the current week of pregnancy
- Normal duration of pregnancy: 40 weeks (280 days)
- : live birth before the completion of 37 weeks (< 37 0/7) of pregnancy
- Post-term birth: live birth after 42 weeks (> 42 0/7) of pregnancy
|Day 0|| |
|Days 6–14|| |
|Week 3|| |
|From week 9|| |
The earlier disruptions take place during fetal development, the more complicated the resulting congenital anomalies!
- All women with reproductive potential should be asked about their intention to become pregnant; by their healthcare provider; all those planning to become pregnant should be counseled.
- Prenatal counseling aims at:
- Identifying and addressing any modifiable risk factors for the woman, future pregnancy, and the fetus
- Educating a woman about the risk factors and options for their reduction or elimination
General chronic diseases: review history and identify chronic medical conditions which may affect the pregnancy (e.g., hypothyroidism, diabetes mellitus, chronic hypertension, etc.)
- Diabetes mellitus
- Review history of psychiatric disorders
- Inform about the risks of untreated mental illness and risk of treatments for pregnancy.
- Screen women with no history of mental conditions for anxiety and depression.
- Family history of heritable conditions: assess family history of genetic conditions and cancer (e.g., breast, uterine, colon cancer) and refer couples with a positive history for counseling.
- Communicable diseases
- Review current medications including herbal products and nutritional supplements.
- Discontinue and switch to safer medications when possible.
- Evaluate a patient's drug regimen and consider the lowest dose of medications necessary to control a patient's condition(s).
- Tetanus, diphtheria, and pertussis: Vaccinate all women before pregnancy according to the guidelines for nonpregnant women (see ).
- Hepatitis B: Vaccinate women with high risk for hepatitis B (see ).
- Influenza: Administer annual to all women.
- Recommend maintaining a normal body weight prior to conception.
- Encourage regular moderate-intensity exercise.
- Screen for sufficient intake of macronutrients and micronutrients such as calcium, iron, vitamin B12, vitamin B, vitamin D, etc.
- Ensure vitamin A is not taken in excess.
- Recommend intake of 0.4 mg of folic acid daily, ideally 4 weeks prior to pregnancy and continue for at least the first 2–3 months of pregnancy.
- Substance use
- Screen all women for alcohol, tobacco, and drug use and educate about associated adverse effects for the maternal and fetal pregnancy outcomes.
- Provide assistance and/or refer to the proper specialists for smoking cessation and alcohol and drug use discontinuation.
Management of exposures
- Exposures to harmful agents
- Advise patients to assess workspace and household for potentially harmful agents (e.g., heavy metals, solvents, chemicals, etc.).
- 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.
- In case ongoing abuse is identified, providers should:
- Provide community resources to the patient.
- Report the case as appropriate.
Pregnancy test: measurement of human chorionic gonadotropin (beta-hCG)
- Urine beta-hCG test (e.g., home pregnancy test)
Serum beta-hCG test (quantitative, high sensitivity)
- Detectable 6–9 days (on average) after fertilization
Normal pregnancy: beta-hCG concentration doubles every 2.5 days in early pregnancy (for the first 4 weeks) 
- Peaks at 10 weeks of gestation (peak value: ∼100,000 mlU/mL)
- ↓ During 2nd trimester
- ↔︎ During 3rd trimester
- At beta-hCG level of 1,500–2,000 mlU/mL pregnancy is visible with transvaginal ultrasound (if beta-hCG < 1000 mlU/mL, repeat beta-hCG and transvaginal ultrasound in 2–3 days)
- Low levels or slow rise in level may indicate
- High levels or fast rise in level may indicate
- Beta-hCG secreting tumors ( , )
- False-positive test results:
Ultrasound findings in normal pregnancy (abdominal or transvaginal)
- At 5–6 weeks of pregnancy: detection of the embryo
- At 10–12 weeks of pregnancy: detection of fetal heartbeat with Doppler ultrasound
- At 18–20 weeks of pregnancy: fetal movements
Transvaginal ultrasound findings
|Weeks after last menstruation (gestational age)||β-hCG mlU/mL|
|Yolk sac||5 ||2500|
|Fetal heartbeat||10 ||17000|
Gestational age and estimated date of delivery
- Gestational age: the age (in weeks and days) of the fetus 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)
Naegele's rule: used to calculate the date of delivery (due date)
- First day of the last menstrual period + 7 days + 1 year - 3 months
- Inaccurate if:
- The date of the last menstrual period is uncertain or unknown.
- The patient has irregular menstruation cycles.
- The patient conceived while taking contraceptive pills.
- Ultrasound: more accurate than Naegele's rule
- gestational age : correlates with the
Numerous physiological changes occur during pregnancy in order to support fetal growth and prepare for delivery.
|Mammary glands|| |
|Vulva and vagina|
- Nutritional intake: needs to be adapted to meet both the demands of the mother and the fetus.
- Limit caffeine intake: daily recommended dose < 200 mg
- Avoid alcohol and tobacco use throughout pregnancy
- Avoid unwashed or uncooked foods
- Raw fish (contamination with parasites and bacteria) and seafood of unknown origin (methylmercury contamination)
- Raw milk products: high risk of
- Raw meat: high risk of
- Supplementation of vitamins and minerals: recommended (see table below)
|Recommended vitamin and mineral supplementation in pregnancy|
|Supplementation||Reason for increased demand||Consequences of deficiency|
|Folic acid || |
|Vitamin B12|| || || |
|Iron || || |
|Calcium || || |
|Iodine || || || |
- The recommendations are determined by the BMI prior to the pregnancy:
- Average recommended daily calorie intake:
- Regular physical activity is recommended (see the Physical activity during pregnancy section below).
- Regular physical activity (i.e., 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 any exercise program.
- Modifying normal exercise routines may be necessary; activities considered unsafe should be avoided.
|Safe and unsafe activities during pregnancy|
|Safe activities*|| |
|Unsafe activities|| |
* In pregnancies without complications as determined by an obstetrician
** Avoid positions associated with ↓ venous return
*** May be considered safe in women who took part in these exercises before the pregnancy and as determined by an obstetrician
Physical activity should be discontinued if the patient presents with any 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, which are associated with high morbidity and mortality rates. High-risk pregnancies require regular prenatal care to monitor and support the pregnant mother (see ).
Risk factors for a complicated pregnancy
- Family history (medical and obstetric) of complicated pregnancies
- Personal history
- Advanced maternal age (> 35 years)
- First pregnancy
- Multiparity (> 5 births)
- Medical conditions (epilepsy, malignancies) , arterial , ,
- Social and environmental factors (e.g., drug use, stress)
- Pre-existing gynecological conditions: uterine myoma, history of uterine surgery
- Prior complicated pregnancies
- Complications that arise during pregnancy (See “Maternal complications during pregnancy” and “Fetal complications during pregnancy” below.)
- Definition: amount of amniotic fluid < 500 mL in the third trimester
- Intrauterine growth restriction (diminished mobility of the fetus)
- Intrauterine compression and decreased amniotic fluid ingestion → Potter sequence: pulmonary hypoplasia (cause of death due to severe neonatal respiratory insufficiency), craniofacial abnormalities, limb anomalies
- Birth complications (e.g., umbilical cord compression)
- Definition: excessive amniotic fluid volume (> 2000 mL in the third trimester) that results in uterine distention and is associated with an increased risk of fetal complications