I. General

  1. About 4% of pregnancies in US
  2. Usually presents in first pregnancy
  3. May be due to hPL
  4. Risk factors (NEJM 337:1591, 1997--JW)
    1. Obesity
    2. Older age
    3. Asian ancestry
    4. Use of progestin-only oral contraceptives
  5. Associated with risk of diabetes later in life
    1. Risk of subsequent type 2 DM among women with history of gestational DM is higher in women who have an additional pregnancy after the index pregnancy (Lancet 347:227, 1996)

II. Screening & Diagnosis

  1. 1-hour GTT: do 24-28wks; give 50g glucose (don't need to be fasting), check plasma glucose in 1h; should be <140; if not, do 3h GTT
    1. Some suggest doing only if 1 or more risk factor for GDM is present: > 25yo, obesity, a 1st-degree relative with DM, or in an ethnic group w/high risk of DM
  2. 3h GTT: normal diet for 3d; overnight fast; check fasting (should be < 95), then give 100g glu, check at 1h (<180), 2h (<155), 3h (<140): if 2 or more met or exceeded, dx = GDM (note these are new, lower thresholds per ADA standards as of 1999--see Diabetes Care 2002 Jan;25(Suppl 1):S5-20)
  3. Fasting plasma glucose--a cutoff of 86mg/dL had a sensitivity of 81% and specifity of 76% (compared with 59% and 91%, respectively, for 1h GTT > 141) in a series of 520 pregnant pts; a 3h GTT was done in all women and used as the "gold standard" for sensitivity/specificity calculations (BMJ 319:812, 1999--JW)

III. Complications

  1. Higher risk of intrauterine fetal death
  1. Need to do fetal movement counting, biweekly NST starting 34-35wks
  1. Birth defects
  1. Transposition of great arteries
  2. VSD
  3. Neural tube defects
  4. Sacral agenesis
  1. Macrosomia, higher risk of shoulder dystocia
    1. In an observational study of 107 pregnant women with insulin-dependent DM, macrosomia was not associated with measures of glycemia during pregnancy or maternal insulin requirements (Obs. Gyn. 99:537, 2002--AFP)
  2. Delayed fetal lung maturity; L/S ratio is misleading in GDM (artificially high for degree of actual lung maturity)
  3. Postnatal hypoglycemia, polycythemia with consequent jaundice
    1. In an observational study of 107 pregnant women with insulin-dependent DM, neonatal hypoglycemia was not associated with measures of glycemia at prenatal visits but was correlated closely with maternal hyperglycemia in labor (Obs. Gyn. 99:537, 2002--AFP)

IV. Management

  1. Monitoring-Postprandial better than preprandial
    1. 66 women with insulin-requiring diabetes at 30wks were randomized to two monitoring strategies: Check glucose Qac/QHS and adjust insulin to get glucose 60-105 vs. check glucos Qam and postprandially and adjust insulin to get glucose below 140.  Women in the post-prandial monitoring group required more insulin (1.1 vs. 0.9 U/kg/d), and had significantly lower HbA1c, less neonatal hypoglycemia (3% vs 21%), fewer LGA infants (12% vs 42%), and fewer c-sections (12% vs 36%); only one baby in postprandial monitoring group was SGA.  NEJM 333:1237, 1995
  1. "Intensive" management associated with better outcomes than less intensive ones
  1. 300 women 24-32wk singleton pregnancies w/GDM (excluded known anomalies, ob complications, long-term medical tx affecting glucose metabolism) Randomized to intensive tx (restricted-calorie diet, care by endocrinologist and obstetrician, insulin if fasting glu > 80 or 1h postprandial glu > 140) vs. usual care (routine dietary recommendations, BIQ glucose checks; transfer to intensive tx arm if fasting glu > 140 or 1h postprandial glu > 200); Intensive tx group achieved stat. sig. better glycemic control; No sig. diff. in risk of macrosomia, fetal or maternal deaths, congenital anomalies, neonatal hypoglycemia, hypocalcemia, or hyperbilirubinema, or mode of delivery (Am. J. Obs. Gyn. 177:190, 1997-abst)
  2. QID insulin better than BID--392 pregnant diabetic women (274 w/gestational, 118 w/pregestational DM) randomized to insulin BID (regular + NPH) v s. QID (TID regular and HS NPH); the 4-dose group had sig. better glycemic control and, among the gestational DM pts, sig. less incidence of neonatal hypoglycemia, jaundice, and overall neonatal morbidity (BMJ 319:1223, 1999--JW)
  3. In a study of 1000 women at 24-34wks gestation randomized to (dietary counseling, home glucose monitoring, and insulin as needed) vs. no intervention unless sx of hyperglycemia occurred, after adjustment for potential confounders, incidence of (fetal or neonatal death, shoulder dystocia, bone fx, or nerve palsy) were sig. lower in intervention group (1% vs. 4%) (NEJM 352:2477, 2005--JW)
  4. In a study in 958 women with mild GDM (abnormal OGTT and fasting glucose < 95 mg/dL) randomized to an intervention (dietary counseling, glucose monitoring, and insulin if necessary) vs. "standard" prenatal care, there was no sig. diff. in incidence of (perinatal mortality or neonatal complications associated with maternal hyperglycemia) but active-treatment group had sig. lower risk for LGA infants (7% vs.14%) incidence of cesarian (27% vs. 34%), and (preeclampsia or gestational HTN) (9% vs. 14%) (NEJM 361:1339, 2009-JW)
  1. Management of mild gestational DM
    1. In a study in 958 women at 24-31wks gestation with fasting glucose < 95 mg/dL and any of the following on a 3-hour, 100g oral glucose tolerance test: > 180mg/dL at 1h, > 155mg/dL at 2h, or > 140mg/dL at 3h, randomized to "standard prenatal care" vs. the same + (nutrition counseling + insulin if required), there were no sig. diffs in incidence of (perinatal mortality or various other perinatal complications), but active-treatment group had sig. lower incidence of shoulder dystocia (RR 0.37), birth weight > 4kg (RR 0.41), and Cesarean delivery (RR 0.79) ( (NEJM 361:1339, 2009-AFP)
  1. Glyburide for gestational DM
    1. Unlike other sulfonylureas & metformin, does NOT cross placenta in sig. quantities
    2. 404 women with GDM 11-33wks gestation randomized to insulin vs. glyburide; 96% of the glyburide gorup were able to achieve good glycemic control on glyburide monotherapy; no diff. in incidence of macrosomia, c/s, neonatal hypoglycemia, or cord-serum insulin levels.  Cord serum assays for glyburide were all negative (NEJM 343:1134, 2000--JW)
  1. Postpartum testing
  1. Should do 75g fasting OGTT 6-12wks postpartum (check glucose fasting and at 2h; DM = fasting > 125 or 2h > 200; IGT = fasting 110-125 or 2h 140-299)
  2. If normal, annual fasting plasma glucose is recommended