• Ideally starts before conception.
  
• Minimum interval for prenatal visits for women with uncomplicated pregnancies: 4–5 wk until 28 wk of gestation, 2–3 wk from 28–36 wk of gestation, and then weekly until delivery.
  
• Prenatal visit: Initial visit should include comprehensive history, physical examination, and extensive patient education. Subsequent visits assess maternal and fetal well being, maternal weight gain with review of nutritional intake, fundal height, BP, and urine screening for asymptomatic UTI and proteinuria.

Screening Us

• First trimester: Routine screening of an unselected population allows for better estimation of GA, leading to reduced frequency of labor induction for postterm labor and use of tocolysis for suspected preterm labor; detection of multifetal pregnancies, and anatomic “markers” suggestive of increased risk for chromosomal abnormalities or fetal malformations (see below).
  
• Second trimester (anatomy scan): Allows detection of 50%–60% of all congenital anomalies with experienced users. Ideally performed between 18–20 wk gestation.
  
• Third trimester: Current data do not support the routine use of US in the third trimester.

Aneuploidy Screening

Routinely offered to all pregnant women (see screening for fetal chromosomal anomalies below).

Assessment of Gestational Age

• Initial assessment of GA is made based on a careful menstrual history.
  
• The estimated date of confinement (EDC) or estimated date of delivery (EDD) is calculated by adding 7 d to the first day of the LMP and then counting back 3 mo.
  
• Note that conceptual age is not equivalent to GA. For an idealized 28-d menstrual cycle, ovulation occurs approximately 2 wk after the LMP.
  
• This leads to frequent confusion in terminology both before and after delivery.

• Pelvic examination by an experienced provider is accurate in determining GA within 1–2 wk until the second trimester. However, this method is seldom used in isolation to estimate GA.
  
• From 16–18 wk of gestation until 36 wk of gestation, the fundal height in centimeters is roughly equal to GA in weeks. However, this finding is more useful to help monitor fetal growth than it is to estimate GA.
  
• The most accurate measurement of GA currently available is obtained with US examination.
  
  
  
  • Various nomograms of fetal growth and formulas have been developed to estimate GA and are integrated into most modern obstetric US equipment.
    
  • Estimates are most accurate when multiple parameters are used, and nomograms are based on data obtained from fetuses of the same ethnic or racial background living at similar altitudes.
    
  • The most accurate measurement during the first trimester is the crown–rump length (variation of 3–5 d).
    
  • From 14–26 wk, the biparietal diameter (BPD) becomes the most accurate parameter (variation of 7–10 d).
    
  • The femur length (FL) can also be used during the second trimester. It correlates well with the BPD and has a variation of 7–10 d.
    
  • The abdominal circumference (AC) is the most variable parameter commonly measured.
    
  • Formulas integrating measurements of BPD, HC, AC, and FL are more useful than single measurements during the third trimester, although these estimates are still less accurate than earlier dating. Caution should be used in using composite GA assignment (averaging of all biometric parameters) with second trimester US because this will reduce the detection of fetal malformation (BPD may be reduced in fetus affected with spina bifida) and chromosomal abnormalities. (Fetuses with Down syndrome have increased incidence of rhizomelic shortening.)

Assessment of Fetal Lung Maturity

• Fetal lung maturity should be assessed before elective delivery at less than 39 wk unless lung maturity can be inferred from any of the following:
  
  
  
  • Fetal heart tones have been documented for at least 20 wk by non-electronic fetoscope or at least 30 wk by Doppler.
    
  • 36 wk have elapsed since a serum or urine hCG pregnancy test result was reported to be positive.
    
  • US dating during first or second trimester supports a GA of 39 wk or greater.

Biochemical Tests

• Lecithin:sphingomyelin ratio (L:S ratio)
  
  
  
  • Both substances are phospholipids “excreted” from fetal lungs into amniotic fluid.
    
  • Whereas sphingomyelin concentration remains relatively constant throughout pregnancy, lecithin increases from 32–33 wk onward.
    
  • The risk of RDS is low when the L:S ratio is >2.
  
  
• Phosphatidylglycerol (PG)
  
  
  
  • Increases several weeks after lecithin.
    
  • Indicative of advanced fetal lung development because it enhances spread of phospholipids in alveoli.
    
  • Assay for PG is not generally affected by common contaminants in amniotic fluid.
    
  • Result may be reported qualitatively or quantitatively. The risk of RDS is low when the concentration ≥0.3.
  
  
• Fluorescence polarization (eg, TDx-FLM)
  
  
  
  • Uses polarized light to directly measure the concentration of surfactant in amniotic fluid relative to the concentration of albumin.
    
  • Elevated ratio of surfactant to albumin (55 mg of surfactant to 1 g of albumin) reflects fetal lung maturity and a low incidence of RDS.
    
  • Blood and meconium interfere with assay.

Biophysical Tests

• Foam stability index (FSI)
  
  
  
  • Based on the ability of surfactant to produce “foam.”
    
  • Ethanol is added to a sample of amniotic fluid, and the mixture is shaken. If surfactant is present in sufficient quantity, foam will form.
    
  • Serial dilutions are performed to calculate an FSI.
    
  • RDS is extremely unlikely after a positive test result (FSI ≥47).
  
  
• Lamellar body count
  
  
  
  • Concentration of lamellar bodies in amniotic fluid can be measured directly by light microscopy or indirectly by photospectroscopy.
    
  • Lamellar bodies are direct evidence of surfactant production by type II pneumocytes.

Diabetes Mellitus during Pregnancy

• Definition: Carbohydrate intolerance of variable severity with onset or first recognition during pregnancy.
  
• Epidemiology
  
  
  
  • 3%–5% of pregnancies are complicated by DM; of these, 80%–90% represent GDM.
    
  • Risk factors for the development of GDM: Age >25 yr, obesity, family history of type II DM, ethnic group (Hispanic, African American, Native American, South or East Asian or Pacific Island ancestry), persistent glucosuria, hypertension, dyslipidemia, history of prior pregnancies complicated by GDM, idiopathic macrosomia, congenital malformation, or stillbirth.
  
  
• Pathophysiology
  
  
  
  • In normal pregnancy: Decreased glucose tolerance → increased insulin levels → euglycemia.
    
  • In both type II DM and GDM: Decreased hepatic and peripheral insulin sensitivity and relatively decreased insulin response.
    
  • GDM is characterized by a 60% decrease in peripheral insulin sensitivity and an inability of the pancreas to produce adequate insulin in response to glucose load.
    
  • Several hormones produced by placenta may antagonize effects of insulin: Somatotropin, progesterone.
  
  
• Signs and symptoms: Identical to signs and symptoms of hyperglycemia in nonpregnant patients (fatigue, polyuria, polydipsia, weight loss, polyphagia, blurred vision).
  
• Diagnosis
  
  
  
  • Screening routinely performed at 24–28 wk GA with 50-g load, 1-h OGTT. Cutoff: 130–140 mg/dL.
    
    
    
    • 140 mg/dL: Sensitivity, 75%; specificity, 85%–94%
      
    • 130 mg/dL: Sensitivity, nearly 100%; specificity, 75%–85%
    
    
  • Abnormal test should be followed by 75-g or 100-g, 3-h diagnostic OGTT. A diagnosis of GDM is established when two or more of the following criteria are met:
    
    
    
    • Fasting blood glucose >95 mg/dL
      
    • 1-h blood glucose >180 mg/dL
      
    • 2-h blood glucose >155 mg/dL
      
    • 3-h blood glucose >140 mg/dL
    
    
  • Women who meet only one of the above criteria should undergo repeat testing during the third trimester.
    
  • Hemoglobin A1C is not a useful test for the diagnosis of GDM because of the increased rate of erythropoiesis during pregnancy.
  
  
• Treatment
  
  
  
  • There are many proposed regimens for glucose monitoring, including self-monitoring of blood glucose with checks before each meal, 1 or 2 h after each meal, and at bedtime.

• Maintaining mean glucose <100 mg/dL during pregnancy reduces perinatal mortality to baseline.
  
• Daily urine tests for ketones.
  
• Weight management for overweight and obese patients.
  
• When pharmacologic therapy is needed to adequately control blood glucose, oral glyburide is most commonly used as the first line therapy in the United States.
  
• Screening the fetus: Perform detailed anatomy US at 18–20 wk and fetal echocardiogram at 20–22 wk. Consider serial US monitoring of fetal size and well-being during the third trimester at 4- to 6-week intervals.