Adverse Pregnancy Outcomes: Classification and Definition
Adverse pregnancy outcomes (APOs) are complications affecting maternal or fetal health during pregnancy, delivery, or the immediate postpartum period, and include: stillbirth, preterm birth (<37 weeks), small-for-gestational-age (SGA) infants, intrauterine growth restriction (IUGR), hypertensive disorders of pregnancy (preeclampsia, eclampsia, gestational hypertension, HELLP syndrome), gestational diabetes, placental abruption, low birth weight infants, pregnancy loss/miscarriage, and neonatal death.
Core Adverse Pregnancy Outcomes
The most consistently recognized APOs across guidelines include:
Fetal/Neonatal Outcomes
- Stillbirth: Fetal death from ≥20 weeks of gestation 1
- Preterm birth: Delivery <37 completed weeks of gestation, with particularly high risk when <34 weeks 1
- Small-for-gestational-age (SGA): Infant birthweight below the 10th percentile for gestational age and sex, used as a proxy for fetal growth restriction 1
- Intrauterine growth restriction (IUGR): Estimated fetal weight <10th percentile for gestational age, often related to suboptimal uterine-placental perfusion 2
- Low birth weight: Infants with reduced weight at delivery 3
- Neonatal death: Death within the first 28 days of life 4
- Congenital malformations and congenital heart block 4
Maternal Outcomes
- Hypertensive disorders of pregnancy: Including preeclampsia (new-onset hypertension with proteinuria after 20 weeks), eclampsia (preeclampsia with seizures), gestational hypertension, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), and chronic hypertension in pregnancy 3, 5, 6
- Gestational diabetes mellitus: Glucose intolerance with onset or first recognition during pregnancy 5, 7
- Placental abruption: Premature separation of placenta from uterus before fetal delivery 5, 7
- Pregnancy loss/miscarriage: Spontaneous pregnancy loss, with recurrent pregnancy loss defined as ≥2 spontaneous miscarriages 5
- Maternal mortality and severe maternal morbidity 3, 8
Clinical Significance
These outcomes are not isolated events but interconnected complications sharing common pathophysiology, particularly placental insufficiency 1. Women experiencing any APO have a 3-fold increased risk of developing cardiovascular disease risk factors within 2 years postpartum 9, with the strongest associations seen between:
- Gestational diabetes and subsequent type 2 diabetes (21-fold increased risk) 9
- Preeclampsia and chronic hypertension (6-fold increased risk) 9
The recurrence risk is substantial: women with prior stillbirth have a 4-fold increased recurrence risk, those with preterm birth have 2.5- to 10.6-fold increased recurrence (nearly 14-fold for PTB <34 weeks), and those with SGA have at least an 8-fold increased recurrence risk 1.
Long-Term Implications
APOs serve as markers for future cardiovascular disease, with women experiencing these complications showing increased risk of stroke (1.74-fold for any hypertensive disorder of pregnancy), myocardial infarction, and cardiovascular mortality that persists for over 40 years after delivery 10, 5, 11. The 2024 AHA/ASA stroke prevention guideline specifically recommends screening for APO history followed by evaluation and management of vascular risk factors 5.
Important Caveats
While these outcomes are traditionally viewed as separate entities, they frequently co-occur and share common antecedents. SGA accounts for up to 50% of preventable stillbirths 1, and many preterm infants are growth restricted 1. The presence of multiple APOs compounds future cardiovascular risk 12. Definitions may vary slightly between studies and healthcare systems, but the core outcomes remain consistent across international guidelines 1, 4, 5, 6.