From Encyclopedia of Sex and Sexuality
The aims of prenatal care are to maintain or improve the health of the mother, reduce the potential complications of pregnancy, and obtain optimum health and safety for the newborn infant. Significant improvements in pregnancy outcome and a reduced incidence in the occurrence of prematurity, stillbirths, and pregnancy losses can be achieved with appropriate prenatal care.
One may consider the concept of a “twelve month” pregnancy. This incorporates preconceptional planning, in which the prospective mother seeks care even prior to attempting to become pregnant. A full and detailed medical history is obtained. When factors that might adversely affect pregnancy are discovered, they are corrected prior to pregnancy.
Work and home histories can often give clues of the presence or absence of dangerous exposure to chemicals or other substances, as an example. A physical examination may bring to light a previously unknown condition or verify a healthy status. Prepregnancy counseling encourages cessation of detrimental habits (e.g., tobacco or drug use), that can lead to pregnancy difficulties or even birth defects. Laboratory testing can discover nutritional problems, such as iron deficiency anemia, or lack of immunity to various diseases, such as rubella (German measles). Other prepregnancy testing that may be appropriate include a cervical cancer screening with a Pap smear and hepatitis screening. When maternal health is found to be optimal, pregnancy is then attempted. Most couples successfully achieve pregnancy within the first year. After conception, the first sign is often a missed menstrual period. Susbsequent visits will again include a history to update events bearing on the conduct of pregnancy, and a repeat physical examination to assure that maternal health and fetal anatomy are normal.
At the time of the first visit following conception, appropriate laboratory studies are performed. These include a complete blood count, a serology test to exclude syphilis (often required by state law), a test for immunity to rubella and a blood type and Rh type. A blood test for exposure to hepatitis and vaginal cultures for infection are commonly performed too. A Pap smear is also obtained for cervical cancer screening if this had not been obtained earlier. During the initial pelvic examination the obstetrician assesses the architecture and the adequacy of the bony pelvis for any potential problems that may arise at the time of vaginal delivery. The estimated due date will be calculated utilizing Naegle’s rule—adding nine months and one week to the first day of the last menstrual period.
By the tenth to twelfth week of pregnancy, counting from the first day of the last menstrual period, the fetal heart beat can usually be detected with a specialized microphone known as a Doppler. At this time the uterus is the size of a medium grapefruit and the fetus can be easily visualized by ultrasound techniques.
For the first six months of an uncomplicated pregnancy, monthly examinations are adequate. At these visits the mother’s weight is recorded, along with her blood pressure and the presence or absence of protein or glucose in the urine. Fetal heart tones are noted. The normal rate is 120–160 beats per minute (the rate is not indicative of the fetus’s sex). The size of the uterus is approximated by abdominal examination to document growth of the fetus during pregnancy.
Between fifteen and twenty-four weeks of pregnancy, a maternal serum alpha feto-protein test is offered. This is a screening blood test for neural tube defects in the infant, such as spina bifida, or open spine. If this screening test indicates possible problems, further testing, such as ultrasound to visualize the defect, is appropriate.
Another special study that can be performed in the middle trimester of pregnancy is amniocentesis, the removal by a syringe and needle of a sample of amniotic fluid surrounding the fetus to determine if the fetal chromosomes are normal. Amniocentesis is generally offered between fourteen and twenty-two weeks of pregnancy to women with a strong family history of genetic disorders, to women thirty-five years of age or older at the time of delivery, and to women in whom some prenatal exam or test suggests a possibility of chromosomal abnormality. This is a low-risk procedure if performed by an experienced obstetrician.
Examination of the fetus by ultrasound is often performed at sixteen to twenty weeks of pregnancy. At this time the fetal anatomy can be examined and sex can be determined in most cases. The volume of amniotic fluid (an index of fetal wellbeing) can be measured, the location of the placenta determined, and the movement and anatomy of the fetus observed.
At the beginning of the third trimester, at approximately seven months of pregnancy, a screening test for diabetes mellitus is commonly performed. This is a blood sugar determination obtained after a glucose-laden beverage is ingested. In some women, glucose intolerance develops during pregnancy due, in part, to hormones manufactured by the placenta. This condition is known as gestational diabetes and is easily managed but important to detect.
After the second trimester, prenatal visits usually increase in frequency; they commonly occur at weekly intervals during the last month of pregnancy. During this time a pelvic examination is usually repeated to check for dilatation and effacement of the cervix, and to document the presenting fetal part—head or feet. If the pregnancy extends beyond forty weeks, prenatal visits may include more in-depth tracing of the fetal heart rate over a period of approximately thirty minutes, sometimes in conjunction with ultrasound testing. The participation and active cooperation of the woman with her doctor will most often result in a comfortable, healthy pregnancy and a healthy baby approximately 266 days after conception.