Seasonality in conception of births and influence on late initiation of prenatal care

doi:10.1016/S0029-7844(01)01362-X

Obstetrics & Gynecology

Volume 97, Issue 6, June 2001, Pages 976-981

https://doi.org/10.1016/S0029-7844(01)01362-X Get rights and content

Abstract

Objective: To determine whether there is a summer peak in conception of births to adolescents (up to 17 years) compared with older teenagers (18–19 years) and adults (20–29 years), and to assess the influence of season of conception on late initiation of prenatal care.

Methods: We analyzed 1,178,607 singleton births to women aged 29 years and younger in Texas between 1994 and 1998. Dates of conception were estimated using last menstrual period and clinical estimates of gestation. Proportions of births conceived per month were assessed for seasonal patterns. Proportions of births with late initiation of prenatal care were also compared by month of conception. The outcomes were further stratified by sociodemographic variables.

Results: There was a consistent summer trough (7.5% in August) and year-end peak (9.1% in December) in conception of births to adolescents (P < .001), a pattern similar to that of older teenagers and adults. Among the adolescents, students and non-Hispanic women giving birth presented a secondary early summer peak (8.8% each in May and June) in their conceptions. There was a modest bimodal effect of season of conception on initiation of prenatal care in all age groups. Adolescent conceptions in April–May and September–October were 14–18% and 6% significantly more likely to have late prenatal care compared with other months, respectively.

Conclusion: Adolescents giving birth in Texas were not more likely to conceive in the summer. They did present seasonal patterns of conception and late initiation of prenatal care similar to older women.

Section snippets

Materials and methods

We undertook a cross-sectional study based on data from computerized live birth certificates without personal identifiers for the state of Texas from 1994 through 1998. There were 1,675,024 registered births during that time and the following exclusions were made: 461,992 (27.6%) women aged 30 years and above, 308 (0.02%) missing information on maternal age; 24,782 (2.5%) twins and higher-order births; and 9335 (0.6%) lacking both last menstrual period (LMP) and clinical estimate of gestation

Results

Among 1,178,607 singleton births to women aged 29 years and less retained in the analyses, 124,005 (10.5%) were births to adolescents (aged 17 years or less), 162,131 (13.8%) to older teenagers, and 892,471 (75.7%) to women aged 20–29 years. The sociodemographic characteristics of these women are presented in Table 1.

Each of the age groups demonstrated a seasonal pattern in conception of births (P < .001) (Figure 1). The peak period of conception occurred from November to January. The month

Discussion

In our study of more than 1.1 million singleton births to Texas women aged 29 years and less at conception, we found a modest but significant monthly variation in the proportion of conceptions. Seasonal patterns were similar for adolescents and older teenagers and not significantly different from adult women. Peaks in conception of live births occurred in March and December among adolescents and older teenagers. Texas vital data do not include information on abortions. To the best of our

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Risk taking behavior, including sexual activity, can be associated with this period of greater free time, and the absence of school structure or supervision. In fact, Tita et al reported a similar small March peak in their population of Texas adolescents when they separated out only the teens who were attending school.14 Different social and school related factors may be important in understanding why seasonal trends might be different even among similar groups of adolescents.15
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View full text

Seasonality in conception of births and influence on late initiation of prenatal care

Abstract

Section snippets

Materials and methods

Results

Discussion

Am J Prev Med

Obstet Gynecol

Teenage pregnancyOverall trends and state-by-state information

Adolescent pregnancy and childbearingLevels and trends in developed countries

Fam Plann Perspect

Association of young maternal age with adverse reproductive outcomes

N Engl J Med

The changing pattern of prenatal care utilization in the United States, 1981–1995, using different prenatal care indices

JAMA

Seasonality of induced abortion in North Carolina

J Biosoc Sci

Demographic components of seasonality of pregnancy

J Biosoc Sci

Seasonal variation in conception and various pregnancy outcomes

Soc Biol