When should a 35-year-old female with a positive home pregnancy test (HPT) and no past medical history schedule her first prenatal visit and what initial laboratory tests are recommended?

First Prenatal Visit Timing and Initial Laboratory Testing

A 35-year-old woman with a positive home pregnancy test should schedule her first prenatal visit as soon as possible, ideally by 8-10 weeks gestation, with comprehensive laboratory testing performed at that initial visit including blood type/antibody screen, complete blood count, hepatitis B surface antigen, HIV, syphilis, rubella immunity, urinalysis with culture, and early glucose screening given her advanced maternal age. 1, 2

Timing of First Prenatal Visit

• Prenatal care should be initiated at 10 weeks gestation or earlier to optimize maternal and fetal outcomes. 2
• Early initiation of care (before 10 weeks) is associated with fewer hospital admissions, improved patient education, greater satisfaction, and lower pregnancy-associated morbidity and mortality. 2
• At age 35, this patient has advanced maternal age, which is independently associated with increased risks of gestational diabetes, hypertension, miscarriage, intrauterine growth restriction, aneuploidy, birth defects, and stillbirth—making early prenatal care particularly important. 2

Essential First Trimester Laboratory Tests

Infectious Disease Screening

• All pregnant women should undergo screening for hepatitis B surface antigen (HBsAg), HIV, syphilis, and rubella immunity at the first prenatal visit. 1
• Hepatitis B screening in the first trimester is critical to recognize and reduce the risk of mother-to-child transmission. 1
• Cervical cultures for sexually transmitted infections and Pap smear (if due per screening guidelines) should be obtained at the initial visit. 1
• Screening for Chlamydia trachomatis is recommended at the first prenatal visit for all pregnant women, with repeat screening during the third trimester recommended for women aged <25 years or those at increased risk. 3

Hematologic Assessment

• Blood typing and antibody screening must be performed at the first prenatal visit to identify potential blood incompatibilities and Rh status. 1
• Complete blood count should be obtained to screen for anemia, as treatment of iron deficiency anemia decreases the risk of preterm delivery, intrauterine growth restriction, and perinatal depression. 1, 2

Metabolic and Diabetes Screening

• Given this patient's age of 35 years, risk assessment for gestational diabetes should be undertaken at the first prenatal visit. 1, 3
• Fasting blood glucose should be measured at the first prenatal visit to screen for pre-existing diabetes. 1
• Women with clinical characteristics consistent with high risk for gestational diabetes (which includes advanced maternal age ≥35 years) should undergo glucose testing as soon as feasible at the first visit. 3, 1
• If initial early screening is negative, repeat testing at 24-28 weeks gestation is mandatory, as this is when gestational diabetes typically develops due to increasing insulin resistance. 3, 1, 4

Renal Function Assessment

• Urinalysis with urine culture should be performed at the first prenatal visit to screen for asymptomatic bacteriuria. 2
• Baseline renal function assessment may be indicated in women with risk factors for preeclampsia or pre-existing medical conditions. 1

Second Trimester Screening (24-28 Weeks)

Gestational Diabetes Screening

• All women with average risk should undergo glucose screening at 24-28 weeks of gestation using either a 50-g glucose challenge test (two-step approach) or a 75-g oral glucose tolerance test (one-step approach). 1, 4
• For the 100-g OGTT diagnostic test, two or more of the following values must be met for diagnosis: fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, 3-hour ≥140 mg/dL. 3

Aneuploidy and Neural Tube Defect Screening

• Maternal serum alpha-fetoprotein (MSAFP) screening for detection of open neural tube defects and anencephaly should be offered between 16-18 weeks gestation. 3, 1
• Multiple marker screening (AFP, hCG, uE3 with or without inhibin-A) should be offered to women unless amniocentesis is indicated based on history/age or they have elected first-trimester screening. 3, 1
• Women 35 years and older should be counseled about the option of amniocentesis for diagnosis of aneuploidy, though multiple marker screening remains an appropriate alternative. 3

Additional Preventive Measures

• Folic acid supplementation (400-800 mcg daily) should be initiated immediately if not already started, as it decreases the risk of neural tube defects. 2
• All pregnant patients should receive tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap), influenza, and COVID-19 vaccines during pregnancy. 2
• Universal screening for depression, anxiety, intimate partner violence, substance use, and food insecurity is recommended early in pregnancy due to the impact of social determinants of health on outcomes. 2

Common Pitfalls to Avoid

• Delaying the first prenatal visit beyond 10 weeks results in missed opportunities for early risk assessment, intervention, and patient education. 2
• Failing to perform early glucose screening in women ≥35 years old may result in delayed diagnosis of pre-existing diabetes, which requires more intensive management than gestational diabetes diagnosed later. 1, 5
• Overlooking the mandatory repeat glucose screening at 24-28 weeks in women who had negative early screening, as insulin resistance increases exponentially in the second and third trimesters. 1, 4
• Relying on fasting glucose alone for diabetes diagnosis—a full oral glucose tolerance test is required for definitive gestational diabetes diagnosis. 5, 4