At what age does the risk for adverse maternal and infant outcomes increase? Nationwide register-based study on first births in Finland in 2005-2014.
BACKGROUND
It is poorly understood if there are specific ages at which adverse outcomes during pregnancy and childbirth start to increase (threshold-ages). The purpose of this study was to examine at which maternal ages the use of maternity care and the risks for adverse maternal and infant outcomes increase.


METHODS
National data from the Finnish Medical Birth Register including all first-time mothers aged 20 years or over with singleton pregnancies in 2005-2014 were analyzed (n = 228 348). Odds ratios for each outcome at different ages were calculated by logistic regression, using women aged 20-24 (n = 56 282) as the reference and adjusting for socioeconomic position and urbanity of residence. The threshold-age was defined as the first significant adjusted odds ratio after which the risk remained significant.


RESULTS
The threshold-ages for use of maternity care varied from 25 years for cesarean section (OR 1.08, 95% CI 1.03-1.14) to 38 years for having 16 or more antenatal visits (1.13, 1.04-1.21). Four threshold-ages were found for maternal health outcomes: 25 years for gestational diabetes (OR 1.15, 1.09-1.23), 27 years for placenta previa (OR 1.75, 1.11-2.75), 33 years for gestational hypertension (1.14, 1.03-1.27), and 38 years for preeclampsia (OR 1.48, 1.12-1.96). The threshold-ages for infant health outcomes varied from 28 years for preterm birth (37 weeks, OR 1.10, 1.02-1.19) to 36 years for perinatal mortality (OR 2.10, 1.44-3.07).


CONCLUSIONS
Different threshold-ages were identified. Most adverse outcomes occurred earlier than the traditional cut-off ages for high risk pregnancy, which have been set at 35 or 40 years.
National Institute for Health and Welfare (THL), Helsinki, Finland.|Department of Public Health, Helsinki University, Helsinki, Finland.
Reija
R
Klemetti
National Institute for Health and Welfare (THL), Helsinki, Finland.|Division of Family Medicine, Department of Neurobiology, Care Sciences and Society, Karolinska Institute, Stockholm, Sweden.
Mika
http://orcid.org/0000-0001-8254-7525
M
Gissler
FCR Blood Service, Helsinki, Finland.
Susanna
S
Sainio
National Institute for Health and Welfare (THL), Helsinki, Finland.|Department of Public Health, Helsinki University, Helsinki, Finland.
Elina
E
Hemminki
D000328:Adult; D002585:Cesarean Section / Q000706:statistics & numerical data; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D016015:Logistic Models; D008423:Maternal Age; D008875:Middle Aged; D016017:Odds Ratio; D054238:Perinatal Mortality; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology / Q000209:etiology*; D012042:Registries; D012307:Risk Factors
Advanced maternal age; adverse infant outcome; adverse maternal outcome; maternity care use; threshold-age