KEY POINTS
• Prenatal care is designed to provide preventive care, active intervention for acute medical problems and identification of social determinants with referral to appropriate programs and assistance for two patients.
• Advances in technology have allowed the fetus to become a separate and distinct patient.
• Patient education is an important component of prenatal care.
BACKGROUND
• Prenatal care is unique:
• It provides care simultaneously to two interdependent patients.
• There are many components of prenatal care:
• Confirming the diagnosis of pregnancy and establishing the estimated gestational age, which allows the estimated date of confinement to be accurately assigned.
• Obtaining a full history and conducting a physical examination with laboratory evaluation.
• Conducting regular periodic examinations with ongoing patient education.
• Assessing and performing well woman health maintenance and preventative care.
• Identifying and addressing pregnancy complications as well as acute medical and psychosocial problems.
• All information obtained should be recorded in a concise manner that is accessible to other members of the health care team in the electronic health record.
DIAGNOSIS OF PREGNANCY AND ACCURATE DATING
• Early pregnancy diagnosis and accurate dating are essential for establishing a prenatal care plan, addressing risk factors, identifying medical complications, and determining appropriate timing of the delivery.
• The diagnosis of pregnancy is facilitated by both presumptive and probable signs.
• Presumptive signs lead a woman to believe that she is pregnant.
• Probable signs are highly suggestive of the diagnosis of pregnancy.
• Note that these signs do not differentiate between an ectopic and an intrauterine pregnancy.
Presumptive Signs
• Amenorrhea is often the first sign of possible conception but may result from other factors, such as anovulation, premature menopause, thyroid disease, or elevated prolactin.
• Subjective signs and symptoms of early pregnancy include breast fullness and tenderness, skin changes, nausea, vomiting, urinary frequency, and fatigue.
• Between 12 and 20 weeks’ gestation, a woman will note an enlarging abdomen and perceive fetal movement.
Probable Signs
• Uterine enlargement
• Softening of the uterine isthmus (Hegar sign)
• Vaginal and cervical cyanosis (Chadwick sign)
• Pregnancy tests:
• Urine pregnancy tests used today are very sensitive and may be positive as early as 5 days after embryo implantation.
• Radioimmunoassay for serum testing of the beta subunit of human chorionic gonadotropin (hCG) may be accurate up to a few days after implantation (or even before the first missed period). hCG production is at its maximum between 60 and 70 days of gestation and declines thereafter.
• These tests do not differentiate between normal pregnancy, gestational trophoblastic disease, ectopic pregnancy, and abnormal intrauterine pregnancy.
• Other bioassay techniques used in the past, such as progesterone withdrawal, are of historic interest only.
Positive Diagnostic Signs
• Fetal heart tones can be detected as early as 7 weeks from the last menstrual period (LMP) by Doppler technology. The nonelectronic fetoscope detects fetal heart tones at 18 to 20 weeks from the LMP.
• Fetal movements (“quickening”) are generally first felt by the patient at approximately 16 to 18 weeks. They are a valuable indication of fetal well-being.
• Ultrasound examination will demonstrate an intrauterine gestational sac at 5 to 6 weeks and a fetal pole with movement and cardiac activity at 6 to 8 weeks. Vaginal probe ultrasonography has made these early measurements even more accurate. Fetal age can be estimated by crown–rump length, and the number of fetuses may be identified. After 12 to 14 weeks of gestation, fetal biometric measurements, including biparietal diameter and femur length, can be used to estimate fetal age accurately. In the second trimester, fetal anatomy, placental location, and amniotic fluid volume can be evaluated. There is no evidence that diagnostic ultrasound exposure has adverse effects on the developing human fetus.
Estimated Date of Delivery
• The expected duration of pregnancy, calculated from the LMP to estimated date of delivery (EDD) is 280 days, or 40 weeks.
• Naegele’s rule is used to calculate the EDD:
• To the 1st day of the LMP, add 7 days and then subtract 3 months.
• Deviations from this calculation may be made for various reasons (e.g., irregular or prolonged menstrual cycles, known single sexual exposure, or known conception date via artificial reproductive technologies, such as in vitro fertilization).
• If the date of the LMP is unknown or does not correlate with uterine size at the first visit, ultrasonography should be used to establish the EDD.
EVALUATION
A complete history and physical examination are performed after the diagnosis of pregnancy is established. An important goal is to develop a trusting, working relationship between the patient and the health care team.
History
• Menstrual and contraceptive history:
• Reliable menstrual history is the most accurate predictor of EDD.
• Gynecologic history: Previous sexually transmitted infections, abnormal Papanicolaou (Pap) smear, gynecologic surgeries, and hospitalization for gynecologic conditions should be recorded.
• Obstetric history:
• The obstetric history is recorded as gravidity and parity. Gravidity is the total number of pregnancies. Parity is expressed as four serial numbers: term deliveries, premature deliveries, abortions and ectopic pregnancy, and living children.
• Details of previous pregnancies, such as character and length of labor, mode of delivery, pregnancy and delivery complications, newborn health, and birth weight, should be noted. Recurrent first-trimester losses may suggest genetic abnormalities in the conceptus or parents while a history of second-trimester losses may suggest genetic abnormalities or cervical insufficiency.
• If the patient has had a cesarean delivery, it is important to document the prior uterine scar type to assist with counseling for delivery mode and timing.
• Medical and surgical history and prior hospitalizations:
• Preexisting medical problems or diagnoses are important for pregnancy risk assessment and management.
• Previous surgeries and hospitalizations should be elicited and evaluated.
• Environmental exposures, medications taken in early pregnancy, history of reactions to medications, legal and illicit drug use, and allergic history.
• Family history of medical illnesses, heritable conditions, genetic abnormalities, mental retardation, congenital anomalies, and multiple gestation.
• Social history:
• Home environment, family and social support, and history of physical or mental abuse should be assessed and appropriate referrals made.
• Assessment of tobacco, alcohol and substance use, abuse, or dependence.
• Review of systems as related to pregnancy: nausea, vomiting, abdominal pain, constipation, headaches, syncopal episodes, vaginal bleeding or discharge, dysuria or urinary frequency, swelling, varicosities, and hemorrhoids.
Physical Examination
• Complete physical examination with attention to specific organ systems as directed by any positive findings in the history:
• Measurement of height, weight, blood pressure, pulse and documentation of prepregnancy body mass index (BMI); funduscopic examination; examination of thyroid, lymph nodes, lungs, heart, breasts, and abdomen, with fundal height and presence of fetal heart tones, extremities; and a basic neurologic exam
• Pelvic examination:
• External genitalia—Evidence of previous obstetric injury should be noted.
• Vagina—Under hormonal influence of pregnancy, cervical secretions are increased, thus raising the vaginal pH, which may cause a change in the bacteriologic flora of the vagina. No treatment is necessary unless diagnosis of a specific infection is made (see “Treatment of Common Lesions and Infections” later in this chapter).
• Cervix—A Pap test as indicated and testing for Chlamydia and gonorrhea are routinely performed.
Cervical softening and eversion (ectropion) is normal.
Nabothian cysts are of no consequence.
Dilatation of the external os is common in multiparous patients and is a nonpathologic finding. Significant cervical effacement or dilation of the internal os is abnormal, except near term, and may indicate premature labor or cervical insufficiency.
Morphologic cervical changes (ridges, hood, or collar), or vaginal adenosis may indicate DES exposure in utero. These women have a higher incidence of cervical insufficiency and preterm delivery and should be evaluated accordingly.
• Uterus—Estimating gestational age by gauging uterine size is one of the most important elements of the initial obstetric examination.
A normal, nongravid uterus is firm, smooth, and approximately 3 × 4 × 7 cm. The uterus will not change noticeably in consistency or size until 5 to 6 weeks after the LMP, or 4 weeks after conception.
Gestational age from the LMP is estimated by uterine volume (i.e., 8 weeks, twice normal size; 10 weeks, three times normal; 12 weeks, four times normal). At 12 weeks, the uterus fills the pelvis so that the fundus of the uterus is palpable at the symphysis pubis. By 16 weeks, the uterus is midway between the symphysis pubis and the umbilicus. At 20 weeks, the uterine fundus is at the level of the umbilicus. Thereafter, there is a rough correlation between weeks of gestation and centimeters of fundal curvature when measured from the top of the symphysis pubis to the top of the uterine fundus (MacDonald measurement).
After correcting for minor discrepancies resulting from adiposity and variation in body shape, a uterine size that exceeds the anticipated gestational age by 3 weeks or more, as calculated from the last normal menstrual period, suggests multiple gestation, molar pregnancy, leiomyomata, uterine anomalies, adnexal masses, or simply an inaccurate date for the LMP. Ultrasonography is the best diagnostic tool for this situation.
Smaller than expected uterine size for gestational age may indicate inaccurate dating or early pregnancy loss.
• Adnexa are difficult to evaluate because the fallopian tubes and the ovaries are lifted out of the pelvis by the enlarging uterus. Any questionable masses should be confirmed by ultrasound evaluation.
• Clinical pelvimetry is performed as part of the initial bimanual exam to assess the general adequacy of the pelvis for vaginal delivery.
Laboratory Evaluation
A history positive for certain illness or abnormalities in other screening tests should be investigated with further tests as indicated.
• A routine initial screen includes a complete blood count, ABO blood typing and Rh factor, red blood cell antibody screening, urinalysis and culture, serologic test for syphilis, rubella titer, Pap test as indicated, cervical testing for gonorrhea and Chlamydia, hepatitis B surface antigen, and testing for HIV.
• Group B Streptococcus (GBS) (see Chapter 23):
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
