Chapter 181 Routine Prenatal Care: First Trimester
Despite the dramatic and vulnerable changes that the conceptus undergoes in the first 14 weeks of gestation, many patients are unaware of their pregnancy or delay seeking prenatal care. Emerging evidence suggests that it is during this period the foundations of a successful pregnancy and even the future health of the adult individual are set. Although most pregnant women would deliver healthy infants without any prenatal care, obstetric care is designed to promote optimal health throughout the course of normal pregnancy while screening for and managing any complications that may develop.
Scope of the Problem: Roughly one fourth of pregnant women do not receive care during the first trimester.
Relevant Pathophysiology: During the first trimester of gestation, the developing embryo implants in the endometrium (except in the case of ectopic pregnancies), the placental attachment to the mother is created, and the major structures and organs of the body are formed. The developing embryo is sensitive to exposures to toxins, medications, and radiation and the effects of maternal conditions that can disrupt this process. Errors in this process may result in major disruptions in structure or function of the fetus or even the complete loss of the pregnancy.
About the 12th week of gestation, the placenta takes over hormonal support for the pregnancy from the corpus luteum. If this transition does not happen smoothly, the pregnancy can be lost.
Strategies: At the first prenatal visit, a comprehensive history should be taken, including previous pregnancy outcome(s), if any, and any medical or surgical conditions that may affect pregnancy. This should include past medical history, information pertinent to genetic screening, and any events in the course of the current pregnancy. Special attention should also be given to diet, tobacco or alcohol use, and any medications or substances used. Routine laboratory studies should be ordered, and the patient should be given instructions concerning routine prenatal care, warning signs of complications, and who to contact with questions or problems. A complete physical examination should be performed, including a Pap test and tests for sexually transmitted diseases.
It is important early in the course of pregnancy to establish an accurate gestational age and estimated date of confinement (EDC, or due date). This information is needed to manage later complications of pregnancy and to determine the timing of evaluations (e.g., neural tube screening, 1-hour glucose challenge testing, Rh prophylaxis). If needed, transvaginal and transabdominal ultrasonographic techniques allow gestational age determination with approximately 7- to 10-day accuracy when performed during the first trimester.
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