title: Effect of maternal age on pregnancy: a retrospective cohort study.
abstract: BACKGROUND
  In the last few decades, there has been a delay in first-time pregnancies, and the average age of women at the time of delivery has increased in many countries. Advanced maternal age is associated with adverse pregnancy outcomes. This study aimed to determine the present trends and pregnancy outcomes related to maternal age in China.
  
  
  METHODS
  Data were collected from 39 hospitals in mainland of China. All deliveries were performed after 28 completed weeks of gestation and between January 1 and December 31, 2011. In total, 110 450 of 112 441 cases were included in the study. All enrolled cases were divided into 6 age groups with 5-year intervals. The χ(2) test or Fisher's exact test and unadjusted binary-Logistic regression were used for statistical analysis.
  
  
  RESULTS
  The mean age at the time of delivery was 28.18 ± 4.70 years (range, 14-52 years). The teenage group (15-19 years) had a higher risk than the 25-29-year old group for anemia (odds ratio (OR), 1.4), preeclampsia (OR, 1.6), preterm birth (OR, 2.1), low birth weight neonates (OR, 2.3), and perinatal mortality (OR, 3.6). The 35-39-year old group and ≥ 40-year-old group had a higher risk than the 25-29-year-old group for leiomyoma (OR, 4.2 vs. 5.8), pregestational diabetes (OR, 2.2 vs. 3.8), chronic hypertension (OR, 4.6 vs. 6.5), gestational diabetes (OR, 2.6 vs. 3.5), preeclampsia (OR, 2.5 vs. 3.6), premature delivery (OR, 1.8 vs. 2.4), postpartum hemorrhage (OR, 1.5 vs. 1.7), placenta previa (OR, 2.7 vs. 4.0), placental abruption (OR, 1.4 vs. 2.5), cesarean delivery (OR, 2.1 vs. 2.5), macrosomia (OR, 1.2 vs. 1.2), low birth weight neonates (OR, 1.6 vs. 2.3), and perinatal mortality (OR, 1.6 vs. 3.7).
  
  
  CONCLUSIONS
  Maternal and neonatal risks are higher during the teenage years and at an advanced maternal age; 20-30 years of age is the lowest risk period for pregnancy and delivery.
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing 100026, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing 100026, China. Email: zhangwy9921@hotmail.com.
authors.forename: Weiyuan
authors.initials: W
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000328:Adult; D002585:Cesarean Section; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000453:epidemiology; D012189:Retrospective Studies; D055815:Young Adult