Incorporating heterogeneous intercourse records into time to pregnancy models

Information on the timing of intercourse relative to ovulation can be incorporated into time to pregnancy models to improve the power to detect covariate effects, to estimate the day-specific conception probabilities, and to distinguish between biological and behavioral effects on fecundability, and therefore the probability of conception in a menstrual cycle. In this paper, Bayesian methods are proposed for joint modeling of intercourse behavior and biologic fecundability. The model accommodates a sterile subpopulation of couples, general covariate effects, and heterogeneity among fecund couples in menstrual cycle viability and in frequency of unprotected intercourse. Methods are described for incorporating cycles with varying amounts of intercourse information into a single analysis. A Markov chain Monte Carlo algorithm is outlined for estimation of the posterior distributions of the unknowns. Themethods are applied to data from a North Carolina study of couples attempting pregnancy.     

Sexual violence at first intercourse against women in Moshi, northern Tanzania: prevalence, risk factors, and consequences

To explore the relationship between sexual violence at first intercourse and later sexually transmitted infections (STIs) in Moshi, Tanzania, we analysed data from a representative household survey that comprised face-to-face interviews with 1,835 women and tests for six STIs on biological samples from 1,235 of these women. Overall, 10.9 per cent report forced first intercourse and 15.3 per cent report unwanted first intercourse. Unadjusted analysis shows a relationship between forced first intercourse and STIs (OR: 1.72, 95 per cent CI: 1.19-2.51). Life-course variables mediate this relationship. Significant predictors of having an STI include older age, more sexual partners, and a partner who has children with other women. Coerced first intercourse appears to be associated with changes in the life course of women and with a heightened risk of contracting an STI.     

Seasonal Patterns of Reproduction in Matlab,Bangladesh

In Bangladesh twice as many births occur in December as in July. This paper examines the seasonal patterns of the risks of conception, fetal loss and return of menses post partum in a longitudinal study of 2,300 women in 14 villages of Matlab, Bangladesh. Life tables were estimated for each month of entry event and then ‘period’ life tables were constructed with the risks for a given calendar month. Confirming the results of earlier studies, risks of resumption of menses were higher in November and December, regardless of time elapsed since the last birth. Similarly, there are increased conception risks in the period from February to April for all fecundable women. The time of lowest fetal loss and stillbirth risks is in the cool season, though this variation makes only a minor contribution to the overall seasonality of births. The pattern of fecundability estimated from data on coital frequency did not match the pattern estimated from reported conceptions; these discrepancies imply possible seasonal changes in other parameters of fecundability besides intercourse.     

Frequency and timing of intercourse: Its relation to the probability of conception

Abstract This paper describes a simple study of the chance of conception assuming a fixed-length menstrual cycle, a specific probability distribution for the day of ovulation, and a broad and a narrow fertile period. Eight different patterns of intercourse throughout the cycle are considered with frequency of intercourse ranging between 5 and 12 times per cycle. Results are given in terms of chance of conception and in terms of waiting times until conception.     

Exploring First Sexual Intercourse,Sexual Orientation,and Sexual Health in Men

In this study the characteristics of the sexual debut of men who have sex with men (MSM) and men who have sex with women (MSW) age 35 or younger (N = 1,201) were compared with one another. We investigated whether these characteristics were associated with sexual health and behavior, and to what extent. Compared to MSW, MSM tended to be older when they had their first sexual intercourse; their first sex partner was older, they felt less ready, and they experienced more pain. We also found that they reported a higher number of lifetime sexual partners and less condom use compared to MSW. Similarities were also ascertained, such as the fact that individuals from both groups do not differ significantly regarding how they experienced their first sexual intercourse emotionally. Many differences between these groups should not always be seen as problematic, whereas others still indicate a need for targeted interventions.     

Premarital first births: The influence of the timing of sexual onset versus post-onset risks in the United States

Motivated by long-standing debates between abstinence proponents and sceptics, we examine how socio-economic factors influence premarital first births via: (i) age at first sexual intercourse and (ii) the risk of a premarital first birth following the onset of sexual activity. Factors associated with an earlier age at first intercourse will imply more premarital first births owing to increased exposure to risk, but many of these same factors will also be associated with higher risks of a premarital first birth following onset. Our analyses confirm previous findings that women from disadvantaged backgrounds are younger at first intercourse and have higher premarital first-birth risks than women from more advantaged backgrounds. However, differences in onset timing have a strikingly smaller influence on premarital first-birth probabilities than do differences in post-onset risks. Our findings thus suggest that premarital first births result primarily from differences in post-onset risk behaviours as opposed to differences in onset timing.     

Facing Age: Women Growing Older in an Anti-Aging Culture,by Laura H. Clarke

This is a pilot study exploring intimacy and self esteem in older black women. Twenty six married, urban, non-institutionalized African American women over the age of 60 were interviewed in this investigation. Information concerning their intimate relationships with their spouses and its relationship to their self esteem was gathered. Subjective passages are examhed to accent these relationships. These women were, generally, open about the quality of the relationship between themselves and their spouses. They reported relatively high levels of intimate relations. In particular they described the sub-factors of intimacy such as affection, friendship and a sense of empathy to be positively associated with self esteem. Interestingly, higher frequency of sexual intercourse was seen to be negatively associated with self esteem for these older women. Implications of these findings are discussed.     

Television viewing and adolescents' sexual behavior.

Over the past two decades the sexual content on television has increased in frequency and explicitness but has seldom included depiction of the use of contraceptives. Concurrently, the age of initiation of heterosexual intercourse has decreased and the number of teenaged pregnancies has remained high. Are these trends related? This survey of 391 adolescents found that those who chose heavier diets of sexy television shows were more likely than those who viewed a smaller proportion of sexual content on television to have had sexual intercourse. This relationship held regardless of perceived peer encouragement to engage in sex and across race and gender groups. While causal direction is not clear from these data, the relationship suggests that either sexual activity results in increased interest in sexual content in the media and/or that viewing such content leads to sexual activity. In either case, the finding points to the need for further research and increased discussion and portrayal of the use of contraceptives on television.     

Prospective study of birth interval dynamics in rural Bangladesh

Abstract A group of 209 married, fecund women in rural Bangladesh were studied prospectively for 24 months from 1969 to 1971 to define some of the biological and sociological factors relating to fertility performance. These women were selected from a larger study population of 112,000 that had been followed with a daily house-to-house vital registration programme since 1966. The selected women were interviewed bi-weekly and were asked questions about menstruation, pregnancy, lactation, husband's occupational absences, and monthly urine tests for pregnancy were taken. The results for 193 non-contracepting women revealed that the seasonal pattern of births previously observed in this population could be associated with a corresponding seasonal pattern of conceptions and that this was due to a seasonal trend in fecundability. The highest conception rates were in the coolest months of the year. Post-partum lactational amenorrhoea was very prolonged, averaging 17 months for women with a surviving child. The appearance of the first post-partum menstrual flow (onset of ovulation) also had a seasonal trend which could not be adequately explained. The median waiting time to conception, once menstruation had resumed was eight months. This interval was influenced by seasonal fluctuations, as well as by the age of women and by husbands' absences. The foetal wastage rate was 15·0 per 100 conceptions, with 62 per cent of the foetal losses occurring during the second month of gestation. Overall, the average birth interval was 33 months, with the prolonged lactational amenorrhoea accounting for almost 45 per cent of this interval. From the Department of Population Dynamics, Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland 21205.     

Power and negotiation: Young women’s choices about sex and contraception

This paper explores issues of power and negotiation for two decisions affecting young women’s sexual lives: die decision to have sexual intercourse and the decision to contracept. Using data from two recent Australian surveys the paper explores the complexity of these decisions and the way in which gender relations between young people can influence dieir reproductive outcomes; young women experience a high rate of sexual coercion and violence and current data collections do not allow analysis of their cause.     

Neighborhood context and racial differences in early adolescent sexual activity

Evidence suggests that African American youths initiate sexual activity at earlier ages than do European American or Latino youths. Using data from a multilevel study in Chicago, we developed and tested a neighborhood-based model of the timing of first adolescent intercourse that emphasizes the impact of neighborhood structural disadvantage and collective efficacy on early sexual activity (at ages 11 to 16). In turn, we explored the extent to which neighborhood factors account for racial differences in the timing of first intercourse. The findings indicate that demographic background, family processes, peer influences, and developmental risk factors account for about 30% of the baseline increased likelihood of early sexual onset for African American youths compared with European American youths. However, a significant residual racial difference remained even after we considered a host of micro-level factors. Neighborhood-level concentrated poverty largely explained this residual racial difference. Collective efficacy also independently contributed to the delay of sexual onset. No significant baseline difference in age of sexual initiation was found between Latino and European American youths.     

生育率变动的综合分析

生育率的变动是各种因素综合影响的结果，这些因素直接和间接作用于生育过程的四个主要环节—性交、受孕、妊娠、分娩，最终影响着生育率的变动。     

Measurement issues involved in examining contraceptive use among young single women

The objective of this study was to determine how research findings on contraceptive use among young single women are affected by differing operational definitions of contraceptive use. Data were analyzed from a student sample and a clinic sample. In the analysis of the student sample were 244 high school and college women aged 16–22 who had experienced sexual intercourse. In the birth control clinic sample were 432 women aged 13–20. Six operational definitions of contraceptive use were analyzed. Correlation and multiple regression analyses were used to examine the relationship of predictor variables with the six definitions separately for each sample. The variance explained for each of the contraceptive measures ranged from 8 percent to 44 percent in the student sample and from 9 percent to 24 percent in the clinic sample.     

Prospective study of birth interval dynamics in rural Bangladesh

A group of 209 married, fecund women in rural Bangladesh were studied prospectively for 24 months from 1969 to 1971 to define some of the biological and sociological factors relating to fertility performance. These women were selected from a larger study population of 112,000 that had been followed with a daily house-to-house vital registration programme since 1966. The selected women were interviewed bi-weekly and were asked questions about menstruation, pregnancy, lactation, husband's occupational absences, and monthly urine tests for pregnancy were taken. The results for 193 non-contracepting women revealed that the seasonal pattern of births previously observed in this population could be associated with a corresponding seasonal pattern of conceptions and that this was due to a seasonal trend in fecundability. The highest conception rates were in the coolest months of the year. Post-partum lactational amenorrhoea was very prolonged, averaging 17 months for women with a surviving child. The appearance of the first post-partum menstrual flow (onset of ovulation) also had a seasonal trend which could not be adequately explained. The median waiting time to conception, once menstruation had resumed was eight months. This interval was influenced by seasonal fluctuations, as well as by the age of women and by husbands' absences. The foetal wastage rate was 15·0 per 100 conceptions, with 62 per cent of the foetal losses occurring during the second month of gestation. Overall, the average birth interval was 33 months, with the prolonged lactational amenorrhoea accounting for almost 45 per cent of this interval.      

Consideration of future consequences and unprotected anal intercourse among men who have sex with men

This study of men who have sex with men (MSM) examined whether tendencies to consider the future consequences of one's actions were associated with sexual behaviors that place oneself at risk for HIV infection. A total of 339 HIV-negative MSM responded to the Consideration of Future Consequences Scale (CFC; Strathman et al., 1994) and to questions about their anal intercourse practices in the past year. In bivariate analyses, men with a stronger future orientation were less likely to engage in anal intercourse unprotected by a condom (p < .05). Multivariate analyses revealed that CFC accounted for significant variance in three of four measures of unprotected anal sex after statistically controlling for demographic covariates (education, income, ethnicity, age). CFC was a better predictor of sexual behavior and accounted for more unique variance than any of the demographic factors. Additional research is needed to confirm that CFC is an antecedent of behavior and to examine the feasibility and efficacy of focusing on CFC in HIV prevention interventions.     

Age at first sexual intercourse, genes, and social context: Evidence from twins and the dopamine D4 receptor gene

We carried out two distinct types of genetic analysis with data from the National Longitudinal Study of Adolescent Health. The first was a non-DNA twin analysis using monozygotic (identical) and same-sex dizygotic (fraternal) twins. The second analysis investigates the association between age at first sexual intercourse and the 48-bp repeat polymorphism in the dopamine receptor D4 gene (DRD4). The twin analysis shows that MZ twins correlate their timing of first sex to a much greater extent than do the same-sex DZ twins. Our analysis of the polymorphisms in DRD4 indicates that those with an any-3R genotype experienced a risk of first sexual intercourse 23% (p = .016), 233% (p = .0001), 28% (p = .012), and 69% (p = .006) higher than those with an other/other (or any-4R) genotype in the all-ethnicities (n = 2,552), Asian, white, and Hispanic samples, respectively. The risk of first sex does not differ between the two genotypes in the African American sample. These results were obtained after adjusting the standard socioeconomic covariates, including gender, parental education, family structure, and community poverty in the regression model. Evidence from both twin and genetic-variant analyses points to a role of genes in the timing of first sexual intercourse.     

Dynamics of contraceptive use and breastfeeding during the post-partum period in Peru and Indonesia

This paper examines the interaction between contraceptive use and breastfeeding in relation to resumption of intercourse and duration of amenorrhea post-partum. We used data from the month-by-month calendar of reproductive events from Demographic and Health Surveys (DHS) in Peru and Indonesia. The analyses show that breastfeeding women were less likely than non-breastfeeding women to have resumed sexual intercourse in the early months post-partum in both countries. In Peru, but not in Indonesia, breastfeeding women had a significantly lower odds than non-breastfeeding women of adopting contraception. Although the likelihood of contraceptive adoption was highest in the month women resumed menstruation in both countries, about ten per cent of subsequent pregnancies occurred to women before they resumed menses. These results emphasize the importance of integrating breastfeeding counselling and family planning services in programmes serving post-partum women, as a means of enabling those who wish to space their next birth to avoid exposure to the risk of a pregnancy that may precede the return of menses.