Medical brain notes 42

  Postterm Pregnancy Normal  full-term  pregnancy  lasts  from  38  to  42 weeks. The “due date” or “estimated date ofdelivery” (EDD) is calculated to be 40 weeks from the first day of the last menstrual period (LMP), presum-  ing regular, 28-day cycles, and without recent, prior use of oral contraceptives.  Postterm pregnancy is a pregnancy thatpersists beyond 42 completed weeks of gestation.  This conditionoccurs in approximately 10% of pregnancies and carries with it an increased risk of adverse outcome. The increased morbidity and mortality in a small percentage of cases, however, warrants careful evaluation of all postterm preg-nancies. In addition, postterm pregnancies can create sig-nificant stress for the patient, her family, and those caring for her. Therefore, the physician should understand the condition and the options for management.   “Postdates” is a commonly used, but misleading synonym, and should be avoided.

  CAUSE   The most common “cause” of postterm pregnancy is inaccurate estimation of gestational age (dating.)  Inaccurate dating ismore likely in women with irregular menses and, thus, in-consistent ovulation; women who seek prenatal care later in pregnancy; women with delayed ovulation (for exam-ple, women who have recently discontinued oral contra-ceptives); and women who inaccurately recall their LMP. Inaccurate dating that leads to the erroneous classification of a pregnancy as postterm has important sequelae. These pregnancies are labeled “high-risk.” Costly increased eval-uations are undertaken and the likelihood of intervention increases, specifically, delivery by induction of labor or by cesarean section, which are potentially associated with increased maternal and fetal morbidity. Other less common causes of postterm pregnancy are listed in Table 23.1. Whatever the cause, there is a tendency for recurrence of postterm pregnancy.  Approximately 50% of patient...

  EFFECTS   Compared with term pregnancies, the morbidity and mortality rates for both mother and fetus increase several-fold with postterm pregnancy.  Risks of maternal vaginal trauma, labor dysfunc-tion, and cesarean delivery increase. Cesarean delivery car-ries increased risks of infection, bleeding, thromboembolic phenomenon, and visceral injury. Stillbirth and neonatal mortality rates increase steadily after 37 weeks, approach-ing 1 in 300 at 42 weeks, and increasing several-fold as the 44th week approaches. It is impossible to discuss postterm gestations without discussing macrosomia, shoulder dysto-cia, meconium aspiration syndrome (MAS), dysmaturity syndrome, and oligohydramnios, as these comorbidities are closely related. Macrosomia  is defined as an abnormally large infant size,specifically, an infant weighing 4000 g to 4500 g or greater.  It oc-curs in approximately 2.5% to 10% of postterm pregnancies. Maternal obesity, diabetes mellitus, or a previou...

  DIAGNOSIS   The diagnosis of postterm pregnancy rests on establishment of the correct gestational age.   The first step in management of a patient with suspected postterm pregnancy is a careful review of the criteria used to establish the gestational age. The most common infor-mation used to determine gestational age include the pa-tient’s reported LMP and the first trimester ultrasound. Ultrasound is most accurate for determining dating for gestational age when it is performed from 6 to 12 weeks of gestation. If the patient’s LMP predicts an estimated date of delivery (EDD) that is within 10 days of an EDD determined by an ultrasound performed between 12 and 20 weeks of gestation, then the gestational age is consid-ered fairly accurate. Once the EDD is determined, it should not be changed unless more accurate information is disclosed.   With improved access to prenatal care and greater importance placed on accurate gestational age assessment, the percentage of pat...

  MANAGEMENT   Once the gestational age is believed to be firmly established and the patient approaches 41 weeks of gestation, manage-ment options include induction of labor or  antepartumfetal surveillance,  which continue either until spontaneouslabor occurs or until approximately 42 weeks. In the United States, very few pregnancies are allowed to progress beyond 42 weeks and virtually none beyond 43 weeks.  Factors thatinfluence management include the patient’s concerns, the assess-ment of fetal well-being, and the status of the patient’s cervix.  Induction of labor is appropriate if the cervix is favorable and if the patient prefers such management. The risk of failed induction is low with a favorable cervix, and most authorities believe it is low enough to recommend delivery in light of the risk of increased fetal morbidity in the post-term period.   The data on preventing postterm pregnancy are con-troversial. Some studies show that  sweepin...