Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is - in some jurisdictions - combined with gynecology under the discipline known as obstetrics and gynecology (OB-GYN), which is a surgical field.
Main areas
Prenatal care Prenatal care is important in screening for various complications of pregnancy. This includes routine office visits with physical exams and routine lab tests along with telehealth care for women with low-risk pregnancies:
First trimester Routine tests in the first trimester of pregnancy generally include:
Complete blood count Blood type Rh-negative antenatal patients should receive RhoGAM at 28 weeks to prevent Rh disease. Indirect Coombs test (AGT) to assess risk of hemolytic disease of the newborn Rapid plasma reagin test to screen for syphilis Rubella antibody screen HBsAg test to screen for hepatitis B Testing for chlamydia (and gonorrhea when indicated Mantoux test for tuberculosis Urinalysis and culture HIV screen Genetic screening for Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18), the national standard in the United States, is rapidly evolving away from the AFP-quad screen, done typically in the second trimester at 16–18 weeks. The newer integrated screen (formerly called F.A.S.T.E.R for First And Second Trimester Early Results) can be done at 10 plus weeks to 13 plus weeks with an ultrasound of the fetal neck (thicker nuchal skin correlates with higher risk of Down syndrome being present) and two chemicals (analytes), pregnancy-associated plasma protein A and human chorionic gonadotropin (pregnancy hormone level itself). It gives an accurate risk profile very early. A second blood screen at 15 to 20 weeks refines the risk more accurately. The cost is higher than an "AFP-quad" screen due to the ultrasound and second blood test, but it is quoted to have a 93% pick up rate as opposed to 88% for the standard AFP/QS. This is an evolving standard of care in the United States.
Second trimester MSAFP/quad. screen (four simultaneous blood tests) (maternal serum AFP, inhibin A, estriol, and βHCG) – elevations, low numbers or odd patterns correlate with neural tube defect risk and increased risks of trisomy 18 or trisomy 21 Ultrasound, either abdominal or transvaginal, to assess cervix, placenta, fluid, and baby Amniocentesis is the national standard for women over 35 or who reach 35 by mid-pregnancy or who are at increased risk due to family history or prior birth history.
Third trimester Hematocrit (if low, the mother receives iron supplements) Group B Streptococcus screen. If positive, the woman receives IV penicillin or ampicillin while in labor—or, if she is allergic to penicillin, an alternative therapy, such as IV clindamycin or IV vancomycin. Glucose loading test (GLT) – screens for gestational diabetes; if > 140 mg/dL, a glucose tolerance test (GTT) is administered; a fasting glucose > 105 mg/dL suggests gestational diabetes. Most doctors do a sugar load in a drink form of 50 grams of glucose in cola, lime or orange and draw blood an hour later (plus or minus 5 minutes). The standard modified criteria have been lowered to 135 since the late 1980s.
Fetal assessments
Obstetric ultrasonography is routinely used for dating the gestational age of a pregnancy from the size of the fetus, determining the number of fetuses and placentae, evaluating for an ectopic pregnancy and first trimester bleeding, with the most accurate dating being in the first trimester before the growth of the fetus has been significantly influenced by other factors. Ultrasound is also used for detecting congenital anomalies (or other foetal anomalies) and determining the biophysical profiles (BPP), which are generally easier to detect in the second trimester when the foetal structures are larger and more developed. X-rays and computerized tomography (CT) are not used, especially in the first trimester, due to the ionizing radiation, which has teratogenic effects on the foetus. No effects of magnetic resonance imaging (MRI) on the foetus have been demonstrated, but this technique is too expensive for routine observation. Instead, obstetric ultrasonography is the imaging method of choice in the first trimester and throughout the pregnancy, because it emits no radiation, is portable, and allows for real-time imaging. The safety of frequent ultrasound scanning has not been confirmed. Despite this, increasing numbers of women are choosing to have additional scans for no medical purpose, such as gender scans, 3D, and 4D scans. A normal gestation would reveal a gestational sac, yolk sac, and fetal pole. The gestational age can be assessed by evaluating the mean gestational sac diameter (MGD) before week 6, and the crown-rump length after week 6. Multiple gestation is evaluated by the number of placentae and amniotic sacs present. Other tools used for assessment include:
Fetal screening is used to help assess the viability of the fetus, as well as congenital abnormalities. Fetal karyotype can be used for the screening of genetic diseases. This can be obtained via amniocentesis or chorionic villus sampling (CVS) Foetal haematocrit for the assessment of foetal anemia, Rh isoimmunization, or hydrops can be determined by percutaneous umbilical blood sampling (PUBS), which is done by placing a needle through the abdomen into the uterus and taking a portion of the umbilical cord. Fetal lung maturity is associated with how much surfactant the fetus is producing. Reduced production of surfactant indicates decreased lung maturity and is a high-risk factor for infant respiratory distress syndrome. Typically, a lecithin:sphingomyelin ratio greater than 1.5 is associated with increased lung maturity. Nonstress test (NST) for fetal heart rate Oxytocin challenge test
Diseases in pregnancy
A pregnant woman may have a pre-existing disease, that may become worse or become a risk to the pregnancy, or to postnatal development of the offspring
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