Pregnancy risks by trimester
Organ development, placentation, and fetal growth have time-sensitive vulnerabilities. Prevention and early detection are emphasized.
Trimester 1 (0–13+6 weeks)
- Neural tube closure occurs early; folic acid has maximal preventive effect when started preconception/early.[3]
- Teratogens: alcohol (FASD), some medications, infections, severe uncontrolled diabetes.
- Screening: dating ultrasound; aneuploidy screening per setting.
- Miscarriage risk is highest (often chromosomal).
Trimester 2 (14–27+6 weeks)
- Anatomy ultrasound (often 18–22 weeks): structural anomalies (heart, neural tube, abdominal wall).
- Placental disease: hypertensive disorders and fetal growth restriction pathways may emerge.
- Maternal supplementation: iron/folate to prevent anemia and support fetal growth.[1][2]
- Preterm birth risk assessment (history, cervix length where used).
Trimester 3 (≥28 weeks)
- Growth & wellbeing: growth restriction, macrosomia, reduced fetal movements.
- Stillbirth: WHO definition for international comparison uses ≥28 weeks.[15]
- Delivery planning: place of birth, monitoring, neonatal readiness.
- If preterm birth likely: antenatal corticosteroids (commonly 24–33+6 weeks) improve neonatal respiratory outcomes.[6][7]
Maternal risks that affect fetal growth and development
| Risk factor | Typical fetal/placental impact | Common mitigation |
|---|---|---|
| Hypertension / preeclampsia | Placental insufficiency → growth restriction, prematurity, stillbirth risk | BP surveillance, symptom education, timely delivery planning |
| Diabetes | Malformations (pre-existing), macrosomia, hypoglycemia risk, stillbirth risk if uncontrolled | Preconception optimization, screening, glucose targets, fetal growth surveillance |
| Alcohol exposure | FASD: lifelong neurodevelopmental disability; growth restriction | Avoid alcohol entirely[4][5] |
| Folate deficiency | Neural tube defects (spina bifida/anencephaly) | Folic acid supplementation[3] |
| Smoking / air pollution | Growth restriction, abruption risk, preterm birth | Cessation supports; exposure reduction |
Optimal antenatal care (high-level)
- Early booking; structured contacts through pregnancy.[1]
- Iron/folate supplementation; vaccination per setting.[1][2]
- Screening for anemia, hypertension, diabetes; treat promptly.
- Ultrasound for dating and anatomy; targeted imaging when indicated.
- Plan delivery location appropriate to risk (e.g., NICU-capable center for threatened preterm birth).
Stillbirth: key concepts
- Definitions and recording vary; WHO uses ≥28 weeks for international comparison.[15]
- Common pathways: placental insufficiency, infection, congenital anomalies, cord accidents, maternal disease; some remain unexplained.
- Prevention is individualized: manage maternal disease, respond to reduced fetal movements, and optimize timing of delivery in high-risk pregnancies.