Risks and Realities Associated with Early or Delayed Childbearing in New Zealand

Durga S. Rauniyar, New Zealand Ministry of Health

As in other developed countries, New Zealand witnessed the significant changes in reproductive patterns during the last century. In recent years, an increasing number of women in their thirties and fewer women in their teens or twenties are having a child. For instance in the year ended June 2000, the age group 30 to 34 year is the most common age group for childbearing, surpassing the 25 to 29 year age group. This represents a significant departure from the early 1970s, when early marriage and early children were the norm, and the age group 20 to 24 years was the most common age for childbearing. On the other hand, though fewer young women (under age 20) are having babies, yet teenage fertility in New Zealand remains as one of the highest rates among OECD countries. The 1998 rate in New Zealand was similar to the rates in England, Wales and Scotland, but exceeded those in Australia, Canada and the Scandinavian countries. Teenage childbearing has received attention from researchers and policy makers, as this has become a pressing social concern in New Zealand. However, delayed childbearing is also equally important, which poses its own biological risks such as an increased likelihood of medical conditions such as hypertension and diabetes. Though some concerns have been expressed for women having children at the later age, there has been relatively little research done to examine the effects of maternal age (either too early or too later) on their health outcomes for both mothers and children. Research has documented that childbearing either at early age or at later age exposes mothers at higher risk for poor health outcomes during pregnancy and childbirth (Woodward and Horwood 2001, La Grew et al. 1996). Such adverse health outcomes are associated with low birth weight, hypertension, diabetes, early death of infants. In most studies maternal age is treated as a categorical variable grouped as under 15 years, or 16-19 to represent adolescents to assess the effects of maternal age on poor health outcomes. Further research suggests that health risks vary by age even among teenage mothers, with those younger than 15 having the worst outcomes while others have found that older teenagers were not at any significantly increased risk (Reichman and Pagnini 1997). Hence, treating maternal age as a categorical variable to reflect teenage childbearing or delayed childbearing may mask variation within these groups. These findings highlight the importance of understanding at what maternal age, mothers experience higher health risks during pregnancy and childbirth. This study examines the effects of maternal age on poor health outcomes as measured by miscarriages, low birth weight, pregnancy complications, type of birth, birth outcomes and postnatal care. Specifically effects of maternal age are examined for adolescents and compared with older mothers, using age as a continuous variable as well as a finely defined categorical variable -- adolescent ages into several categories for instance, 12-13, 14-15; 16-17; 18-19. While for older age groups, five- year age band is used such as 25-29 and so forth. The study uses data from the newly established Maternal and Newborn Information System (NMIS), whose primary purpose is to improve the health of New Zealand children and mothers. National maternity data have been collected in New Zealand for some years, but only in 1999, the NMIS is established which is a collection of perinatal information, by amalgamating data from Lead Maternity Carer (LMC) payment claims and the data collected at the hospital discharge through the National Minimum Dataset (NMDS). Findings of this study may have implications for defining teenagers. In New Zealand, the definition of teenage pregnancy has been used inconsistently between age 13 and 19 years, for instance, Statistics New Zealand defines teenagers from age 15 to 19 years while others including the Ministry of Health uses the age band of 16-19 years. Some studies include 13 to 21 years, such inconsistencies in the use of the adolescent age group may lead inconclusive results. In addition, the study findings may contribute in understand the extent of risk associated with maternal age. Preliminary results show that 53,273 children were born in New Zealand hospitals in 1999 of which 440 were still births and 129 perinatal deaths. About 8 percent births occurred among young mothers aged 16-19, while only 0.2 percent births occurred among mothers younger than 16 years. At the older ages, about 12 percent births occurred among 35-39 years and 2 percent among 40 years and older mothers. Women at the both ends of reproductive life have the highest rates of miscarriage. The preliminary results suggest a number of associations with the rate of caesarean sections including an increasing maternal age and number of nulliparous women, a fall in gravidity and a changing ethnicity. Age is associated with the method of delivery. Seven percent of babies were born pre-term in 1999. Teenagers shared about 9 percent of still births alike the mothers of 35-39 years. Gestational-age as well as maternal age are strongly associated with birth weight. Results from multivariate analysis and details of findings will be presented in the full paper.