A 32-year-old poorly controlled diabetic G2P1 is undergoing amniocentesis at 38 weeks for fetal lung maturity prior to having a repeat cesarean delivery.
Which of the following laboratory tests results on the amniotic fluid would best indicate that the fetal lungs are mature?
The lecithin-to-sphingomyelin (L/S) ratio in amniotic fluid is close to 1 until about 34 weeks of gestation, when the concentration of lecithin begins to rise. For pregnancies of unknown duration but otherwise uncomplicated, the risk of respiratory distress syndrome (RDS) is relatively low when the L/S is at least 2:1. Maternal hypertensive disorders and fetal growth retardation may accelerate the rate of fetal pulmonary maturation, possibly as a result of chronic fetal stress. A delay in fetal pulmonary maturation is observed in pregnancies complicated by maternal diabetes or erythroblastosis fetalis. A risk of RDS of 40% exists with an L/S ratio of 1.5:2; when the L/S ratio is less than 1.5, the risk of RDS is 73%. When the L/S ratio is greater than 2, the risk of RDS is slight. However, when the fetus is likely to have a serious metabolic compromise at birth (eg, diabetes or sepsis), RDS may develop even with a mature L/S ratio (> 2.0). This may be explained by lack of PG, a phospholipid that enhances surfactant properties. The identification of PG in amniotic fluid provides considerable reassurance (but not an absolute guarantee) that RDS will not develop. Moreover, contamination of amniotic fluid by blood, meconium, or vaginal secretions will not alter PG measurements.
A 26-year-old G1P0 patient at 34 weeks’ gestation is being evaluated with Doppler ultrasound studies of the fetal umbilical arteries. The patient is a healthy smoker. Her fetus has shown evidence of intrauterine growth restriction (IUGR) on previous ultrasound examinations. The Doppler studies currently show that the systolic to diastolic ratio (S/D) in the umbilical arteries is much higher than it was on her last ultrasound 3 weeks ago, and there is now reverse diastolic flow.
Which of the following is correct information to share with the patient?
Simple continuous-wave Doppler ultrasound can be used to display flow velocity waveforms as a function of time. With increased gestational age, in normal pregnancy there is an increase in enddiastolic flow velocity relative to peak systolic velocity, which causes the S/D ratio to decrease with advancing gestation. An increase in S/D ratio is associated with increased resistance in the placental vascular bed, as can be noted in preeclampsia or fetal growth restriction. Nicotine and maternal smoking have also been reported to increase the S/D ratio. Many studies document the value of umbilical Doppler flow studies in recognition of fetal compromise. The S/D ratio increases as the fetal condition deteriorates; this is most severe in cases of absent or reversed end diastolic flow.
A 17-year-old primipara presents to your office at 41 weeks. Her pregnancy has been uncomplicated. Because her cervix is unfavorable for induction of labor, she is being followed with biophysical profile (BPP) testing.
Which of the following is correct information to share with the patient regarding BPPs?
The BPP is based on FHR monitoring with nonstress test (NST) in addition to four parameters observed on real-time ultrasonography—amniotic fluid volume, fetal breathing, fetal body movements, and fetal body tone. Each parameter gets a score of 0 or 2. A score of 8 or 10 is considered normal, a score of 6 is equivocal, and a score of 4 or less is abnormal and prompts delivery. The false-negative rate for the BPP is less than 0.1%, but false-positive results are relatively frequent, with poor specificity. Oligohydramnios is an ominous sign, as are spontaneous decelerations. In patients with profile scores of 8 but with spontaneous decelerations, the rate of cesarean delivery indicated for fetal distress has been 25%. There are no large clinical trials to guide the frequency of testing; however, when the maternal condition is stable and the testing is reassuring, the testing may be repeated at weekly intervals. Certain high risk conditions may prompt more frequent testing.
A patient comes to your office with her last menstrual period 4 weeks ago. She denies any symptoms such as nausea, fatigue, urinary frequency, or breast tenderness. She thinks that she may be pregnant because she has not had her period yet. She is very anxious to find out because she has a history of a previous ectopic pregnancy and wants to be sure to get early prenatal care.
Which of the following actions is most appropriate at this time?
Nausea, fatigue, breast tenderness, and urinary frequency are all common symptoms of pregnancy; however, they are nonspecific symptoms, and are not consistently found in early pregnancy. On physical examination, the pregnant uterus enlarges and becomes more boggy and soft, but these changes are not usually apparent until after 6 weeks’ gestation. In addition, other conditions such as adenomyosis or fibroids may result in an enlarged uterus. Abdominal ultrasound will not demonstrate a gestational sac until a gestational age of 5 to 6 weeks is reached, nor will it detect an ectopic pregnancy at the time of the missed menstrual period. It is therefore not indicated in this patient. A Doppler will detect fetal heart tones usually no sooner than 10 to 12 weeks. A sensitive serum quantitative pregnancy test can detect HCG levels by 8 to 9 days postovulation, and it is therefore the most appropriate next step in the evaluation of this patient.
A patient presents for her first OB visit after having a positive home pregnancy test. She reports her last menstrual period was about 8 weeks ago, but she is not entirely certain because she has a long history of irregular menses. Her urine pregnancy test in your office is positive.
Which of the following is the most accurate way to date this patient’s pregnancy?
Measurement of the fetal crown-rump length is the most accurate means of estimating gestational age. In the first trimester, this ultrasound measurement is accurate to within 3 to 5 days. Estimating the uterine size on physical examination can result in an error of 1 to 2 weeks in the first trimester. Quantification of serum HCG cannot be used to determine gestational age, because at any gestational age the HCG number can vary widely in normal pregnancies. A single serum progesterone level cannot be used to date a pregnancy; however, it can be used to establish that an early pregnancy is developing normally. Serum progesterone levels less than 5 ng/mL usually indicate a nonviable pregnancy, while levels greater than 25 ng/mL indicate a normal intrauterine pregnancy. Progesterone levels in conjunction with quantitative HCG levels are often used to determine the presence of an ectopic pregnancy. Early ultrasound is more reliable than precise knowledge of last menstrual period in determining dates.
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