National Survey of Family Growth: design, estimation, and inference.

The purpose of this report is to document the procedures used in the 1988 National Survey of Family Growth (NSFG) to select the sample, weight the data to produce national estimates, impute missing data, and estimate sampling errors. Therefore, this report necessarily contains a great deal of technical detail. For readers who do not need this level of detail, this summary briefly describes the procedures used. The National Survey of Family Growth is conducted every few years by the National Center for Health Statistics (NCHS), a part of the U.S. Department of Health and Human Services. The purpose of the survey is to collect and publish data from a national sample of women on childbearing, factors affecting childbearing (such as contraception, sterilization, and infertility), and related aspects of maternal and infant health. Interviewing for Cycle IV of the survey was done in 1988 by Westat, Inc., under a contract with NCHS. Personal interviews were conducted between January and August of 1988 with a national sample of 8,450 women in the civilian noninstitutionalized population of the United States. Interviews were conducted in person by trained female interviewers and lasted an average of 70 minutes. The interview focused on the woman's pregnancies, if any; her use of contraception; her ability to bear children (fecundity and infertility); her use of medical services for family planning, infertility, and prenatal care; her marriage and cohabitation history, if any; and a wide range of demographic and economic characteristics. This report describes some of the main methodological aspects of the survey, including the sample design, weighting, sampling errors, and imputation of missing data. These topics will be described briefly and less technically in this summary. Each topic is discussed in more detail in the rest of the report.

Sample design, sampling weights, imputation, and variance estimation in the 1995 National Survey of Family Growth.

OBJECTIVES: Cycle 5 of the National Survey of Family Growth (NSFG) was conducted by the National Center for Health Statistics (NCHS) in 1995. The NSFG collects data on pregnancy, childbearing, and women's health from a national sample of women 15-44 years of age. This report describes how the sample was designed, shows response rates for various subgroups of women, describes how the sampling weights were computed to make national estimates possible, shows how missing data were imputed for a limited set of key variables, and describes the proper ways to estimate sampling errors from the NSFG. The report includes both nontechnical summaries for readers who need only general information and more technical detail for readers who need an in-depth understanding of these topics. METHODS: The 1995 NSFG was based on a national probability sample of women 15-44 years of age in the United States and was drawn from 14,000 households interviewed in the 1993 National Health Interview Survey (NHIS). Of the 13,795 women eligible for the NSFG, 10,847 (79 percent) gave complete interviews. RESULTS: This report recommends using weighted data for analysis and a software package that will estimate sampling errors from complex samples (for example, SUDAAN or comparable software). The rate of missing data in the 1995 NSFG was very low. However, missing data were imputed for 315 key variables, called "recodes." Of the 315 recodes defined for Cycle 5, 271 variables had missing data on less than 1 percent of the cases; only 44 had 1 percent or more with missing data. These missing values were imputed for all of these 315 variables. The imputation procedures are described in this report.

Contraceptive utilization: United States, 1976.

Statistics, based on data collected in 1976, are presented on the use of contraception by currently married women, never-married women with offspring in the household, and widowed, divorced, and separated women. Women who used contraception are shown by the method of contraception used, according to race and age of the woman and by various socioeconomic characteristics.

Fertility, family planning, and women's health: new data from the 1995 National Survey of Family Growth.

OBJECTIVES: This report shows data on a wide range of topics from the 1995 National Survey of Family Growth (NSFG), including: pregnancy and birth, marriage, divorce, cohabitation, sexual intercourse, contraception, infertility, use of family planning and other medical services, and health conditions and behavior. METHODS: The data in this report are based on in-person interviews with a national sample of 10,847 women 15-44 years of age. The interviews lasted an average of 103 minutes. The response rate was 79 percent. The sample data are adjusted for nonresponse and are national estimates. RESULTS: Following large increases in the 1970's and 1980's, the proportion of teenagers who have ever had sexual intercourse decreased slightly between 1990 and 1995; condom use, both at first intercourse and currently, has increased markedly since the 1970's. These changes may have contributed to the decreases in the teen birth rate observed in the 1990's. For all women 15-44 years of age, the number whose partner was currently using the condom (at the date of interview) increased from 3.6 million in 1982 to 5.1 million in 1988 and 7.9 million in 1995. About 8 percent of women reported that their first intercourse was not voluntary. This result is consistent with an earlier national survey. About 20 percent reported that they had been forced by a man to have intercourse at some time in their lives. About 10 percent of births in 1990-95 were unwanted by the mother compared with 12 percent in 1984-88. The decrease in unwanted births was particularly large for black women. It appears that the prevalence of pelvic inflammatory disease (PID) and vaginal douching have both decreased since 1988.

Use of infertility services in the United States.

OBJECTIVE: To examine the characteristics of women in the 1988 National Survey of Family Growth who reported having obtained medical services for impaired fecundity. METHODS: From a national sample of 8450 women between the ages of 15-44, drawn from the civilian, noninstitutionalized population of the entire United States in 1988, we estimated the use of infertility services in the United States. Multivariate statistical modeling was used to identify the characteristics associated with use of infertility services among the 770 women who reported impaired fecundity in this survey. RESULTS: Of all women with impaired fecundity, 43% had obtained some form of infertility service and 24% had obtained specialized infertility treatment--ovulation drugs, treatment of fallopian tubes, artificial insemination, or in vitro fertilization. Older, white, married women of higher socioeconomic status were most likely to have obtained specialized services, and a history of endometriosis was also strongly associated with having received such services. CONCLUSION: Most women with impaired fecundity had not obtained infertility services. Use of specialized services was strongly associated with certain sociodemographic variables or a history of endometriosis.

Characteristics of infertile women in the United States and their use of infertility services.

National estimates of demographic characteristics are shown for infertile women compared with those who were fecund, women with primary versus secondary infertility, and infertile women who had, and had not, sought infertility services. Overall, 30% of infertile women had primary infertility, and 70% had secondary infertility. Women with primary infertility were twice as likely to seek services as women with secondary infertility. Many demographic characteristics of women with secondary infertility who sought services differed from those of women who had not sought services. There were fewer differences among women with primary infertility. These findings have implications for the generalizability of results from clinic-based studies and suggest that more research is needed on the barriers to service among infertile couples.

Cesarean section and subsequent fertility: results from the 1982 National Survey of Family Growth.

The purpose of this article was to examine the question of fertility after a cesarean section. The study design is that of a retrospective cohort study with matched pairs, using the cross-sectional interview data of the 1982 National Survey of Family Growth. The subsequent fertility of 406 women who had had their first delivery by cesarean section is compared with that of 406 matched control women. Using any of several measures, women who had had a cesarean section had lower fertility. The difference in fertility seemed to result largely from difficulties in having children after a cesarean section, rather than lessened desire for children. Sterilizations were more frequent and performed earlier among women who had had a cesarean section than among the control women.

Predictors of high-risk behavior in unmarried American women: adolescent environment as risk factor.

BACKGROUND: Heterosexual intercourse with two or more partners in a short time period represents a high-risk behavior for acquisition and transmission of sexually transmitted pathogens (STDs). Identification of factors that may predict high-risk sexual behavior can help to focus primary prevention strategies on women at risk for future acquisition of infection. METHODS: We analyzed survey data obtained in 1988 from a nationally representative sample of 8,450 American women of reproductive age in order to identify such factors. RESULTS: Of all sexually experienced unmarried women, 6.6% reported having had two or more sexual partners in the preceding three months. Earlier age at first sexual intercourse was associated with multiple recent partners, and with lower reports of abstinence. Birth region in the West, lack of attendance at religious services as an adolescent, and having a mother who had her first child before she was 25 years of age were factors associated with multiple recent partners. Among unmarried white women having a mother who worked full time and not living with both parents during adolescence were associated with multiple recent partners; among unmarried black women, the inverse was true (p for racial difference < .05). Multivariate analysis showed western birth region and earlier age at first sexual intercourse to be significant predictors of having multiple recent sex partners. CONCLUSIONS: Early environment and race influence later sexual behavior. These factors should be considered in targeting and planning education for STD prevention.

Source of service and visit rate for family planning services: United States, 1982.

The factors that affect how women choose their source of family planning care and how often they go for such care were investigated in the National Survey of Family Growth. The survey is based on a national sample of women 15-44 years of age interviewed in 1982, 4,318 of whom had family planning visits in the last 3 years. In contrast, previous research has been based on small, nonrepresentative samples, usually in one or a few locations or limited to visits to either private doctors or clinics, but not both; been limited to teenagers; or had no multivariate analysis. This study overcomes those limitations. When other variables were controlled, race, income, and insurance coverage had important effects on provider choice; marital status was important for white women, but not for black women. Contraceptive method, insurance coverage, and race were important determinants of the frequency of family planning visits, independent of other variables. It is suggested that relative costs or ability to pay, confidentiality, knowledge of alternative sources, and convenience of location affect choice of provider and visit rates.

Factors associated with obtaining health screening among women of reproductive age.

Death and disability associated with breast and cervical cancer and hypertension can be reduced by early detection and treatment. The authors examined the rates for having obtained a Papanicolaou (Pap) test or pelvic examination, a breast physical examination, and a blood pressure test within the last 12 months among women of reproductive age in the United States in 1988, as reported by the 8,450 women interviewed for the 1988 National Survey of Family Growth. Overall, the annual rates of screening for women ages 15-44 years for those tests were 67 percent for a Pap test or pelvic examination, 67 percent for a breast examination, and 82 percent for a blood pressure test. Standard recommendations for the frequency of screening and survey data were examined to see whether actual screening practice was consistent with those recommendations. More than 90 percent of women who had a family planning service visit within 12 months received each of the tests, regardless of who provided the service or who paid for the visit. Women who were not sexually active, women with little education or low income, American Indian women, Hispanic women, and women of Asian or Pacific Islander descent had lower rates of screening than others, regardless of their risk status. These findings strongly suggest that the likelihood of having obtained screening among women 15-44 years old is determined primarily by how often a woman uses health care, rather than by her risk of disease.

Social and clinical correlates of postpartum sterilization in the United States, 1972 and 1980.

This analysis is based on the 1972 and 1980 National Natality Surveys, conducted by the National Center for Health Statistics. About 10.6 percent (381,000) of women in the United States who delivered live infants in 1980 were sterilized postpartum. About 93 percent of these postpartum sterilizations were tubal operations; only 1.4 percent were hysterectomies. Because the literature on the health correlates of sterilization is sparse, this analysis was exploratory. In both 1972 and 1980, married mothers were more likely to be sterilized postpartum if they had previous fetal losses, underlying medical conditions, complications of pregnancy, or a cesarean delivery. Inspection of more detailed tabulations reveals that repeat cesarean delivery, multiparity, diabetes and at the higher birth orders, excess weight gain, and toxemia preeclampsia were associated with postpartum sterilization. An apparent association with varicosity may be due to misreporting. The degree to which each of these associations is causal or spurious awaits further research, but preliminary analysis suggests that some maternal health factors may influence some sterilization decisions. Beyond these specific maternal health conditions and complications, the evidence for a connection between poor maternal health and sterilization is equivocal.

Understanding U.S. fertility: findings from the National Survey of Family Growth, Cycle III.

PIP: The 1st overview of findings from Cycle III of the National Survey of Family Growth, the latest of 7 such surveys of US fertility since 1955 and the 1st to cover all women of childbearing age in the conterminous US is presented. Interviews between August 1982 and February 1983 with 7969 women, representative of 54 million women aged 15-44, reveal that sterilization is now the leading contraceptive method in the US, used by 33% of all contraceptors in 1982 (22%, female sterilization; 11% male sterilization), followed by the pill (29%), condom (12%), diaphragm (8%), and IUD (7%). Linked to this is the continuing decline in unwanted births since the baby boom peak in 1957, which accounted for nearly 1/2 of the drop between 1973 and 1982 in ever-married women's children ever born, from 2.2 to 1.9/woman. However, births conceived sooner than planned increased slightly among younger married women, probably due to the large drop in pill use since 1973 and increased use of the less effective diaphragm and condom among couples still intending to have more children. Black women are now more likely than white women to use the most effective female methods: female sterilization, pill, and IUD. Only 45% of women aged 15-44 in 1982 had used a contraceptive method at 1st intercourse. 4 out of 5 women married for the 1st time between 1975 and 1982 had intercourse before marriage. However, premarital sexual activity may be leveling off among white teenagers after a steep rise since the early 1970s and declining moderately among black teenagers. 16% of 1st marriages among ever-married women aged 15-44 in 1982 had been dissoved within 5 years, mostly by divorce or separation. 59% of black women with children in 1982 had their 1st birth before marriage, compared to 11% of white mothers. The proportion of babies who were breastfed more than doubled between 1970-71 and 1980-81, from 24 to 53%.^ieng

Childlessness in the United States: estimates from the National Survey of Family Growth.

PIP: Using a representative sample of about 17,000 ever married women 15 to 44 years of age, this article presents national estimates of the prevalence and correlates of voluntary, involuntary, and temporary childlessness in the United States. These three groups of childless couples are compared with the parents of small planned families and other parents on a number of social, economic, marital, and family characteristics. When viewed cross sectionally, voluntarily childless couples constitute between 1.3% and 1.8% of currently married couples, depending on the definitions used. They are a distinctive but rare population. Their future prevalence depends primarily on the decisions of the large group of temporarily childless couples.^ieng

Effect of transport on blood selenium and glutathione status in feeder lambs.

Stress from transport may be linked to increased generation of reactive oxygen species, the removal of which requires reduced glutathione and selenium. The aim of this experiment was to examine the effect of transport on glutathione and Se status of feeder lambs. Recently weaned lambs (n = 40) were blocked by gender and BW on d 0 of the experiment and randomly assigned to 2 treatment groups: group 1, no transport and full access to feed and water (control), and group 2, 8-h road transport followed by another 16 h of feed deprivation (transport). After 24 h, both treatment groups were treated the same. All lambs were weighed, and blood samples were collected at 0, 8, 24, and 72 h and analyzed for whole-blood (WB) and serum Se concentrations, serum NEFA concentrations, and erythrocyte concentrations of glutathione. Transport of feeder lambs for 8 h followed by another 16 h of feed deprivation transiently (significant at 24 h but no longer different at 72 h) decreased BW and erythrocyte glutathione concentrations and increased serum NEFA and blood Se concentrations compared with control lambs. Our results suggest that 8 h of transport followed by another 16 h of feed deprivation results in fatty acid and Se mobilization from tissue stores with a coincident decrease in erythrocyte glutathione concentrations.

Organic and inorganic selenium: IV. passive transfer of immunoglobulin from ewe to lamb.

Newborn lambs depend on their dams for passive transfer of immunoglobulins, primarily IgG, for protection from harmful pathogens until their own immunological defenses have developed. Previous studies have suggested that supplementation with Se results in a modest increase in IgG concentration in serum of newborn calves and lambs. To evaluate the effect of the Se source and supplementation rate in ewes during pregnancy on passive transfer of IgG to their lambs, 210 Polypay, Suffolk, or Suffolk × Polypay cross ewes were divided into 7 treatment groups (n = 30 each) and drenched weekly with no Se, at the maximum FDA-allowed concentration with inorganic Na-selenite or organic Se-yeast (4.9 mg Se/wk), or with inorganic Na-selenite and organic Se-yeast at supranutritional concentrations (14.7 and 24.5 mg Se/wk). Ewe serum IgG concentrations were measured within 30 d of parturition, ewe colostrum and lamb serum IgG concentrations were measured at parturition before suckling, and lamb serum IgG concentrations were measured again at 48 h postnatal. Ewes receiving 24.5 mg Se/wk tended to have or had, independent of Se source, greater colostral IgG concentrations than ewes receiving 4.9 mg Se/wk overall (81.3 vs. 66.2 mg/mL; P = 0.08) and for Polypay ewes only (90.1 vs. 60.7 mg/mL; P = 0.03). Polypay ewes receiving Se-yeast at 24.5 mg Se/wk transferred a greater calculated total IgG amount to their lambs than Polypay ewes receiving Se-yeast at 4.9 mg Se/wk (15.5 vs. 11.6 g; P = 0.02), whereas the converse was true (interaction between Se source and dose concentration; P = 0.03) for Polypay ewes receiving inorganic Na-selenite at 24.5 mg Se/wk vs. Na-selenite at 4.9 mg/wk (11.6 vs. 15.7 g; P = 0.08). Our results suggest that supranutritional Se supplementation of Polypay ewes during pregnancy increases colostral IgG concentrations but that the optimal supplementation rate for IgG transfer from ewe to lamb may differ for Na-selenite and Se-yeast.

Organic and inorganic selenium: III. Ewe and progeny performance.

Selenium is an essential micronutrient in sheep, and deficiency can limit lamb growth and survival. To evaluate how different chemical forms of Se administered to mature ewes at comparative dosages affect ewe and progeny performance, 240 ewes were divided into 8 treatment groups (n = 30 each) and drenched weekly with no Se; at the maximum FDA-allowed concentration with inorganic Na-selenite or organic Se-yeast (4.9 mg Se/wk); with inorganic Na-selenate (8.95 mg Se/wk); or with inorganic Na-selenite and organic Se-yeast at supranutritional concentrations (14.7 and 24.5 mg Se/wk, respectively). The treatment period started approximately 2 wk before breeding and lasted for 62.5 wk. Ewes of the no-Se and Se-yeast groups continued treatments for another 21 to 24 wk through a second lambing season. Chemical form or dosage of Se did not affect ewe reproductive performance based on proportion of ewes lambing in each treatment group, or number of lambs born, nursed, or weaned per ewe (all P > 0.10). Ewes receiving the highest supplementation rate of Se-yeast at 24.5 mg Se/wk had higher BCS (scale 1 to 5) at the end of yr 1 (2.95 vs. 2.66; P = 0.05) than ewes receiving Se-yeast at 4.9 mg Se/wk. Performance was better in lambs from ewes receiving Se-yeast at 24.5 mg Se/wk than in lambs from ewes receiving Se-yeast at 4.9 mg Se/wk or no Se. In yr 1, lambs from ewes receiving Se-yeast at 24.5 vs. 4.9 mg Se/wk were heavier at 120 d of age (37.0 vs. 34.2 kg; P = 0.05). In yr 2, lambs from ewes receiving Se-yeast at 24.5 mg Se/wk were or tended to be heavier at 60 d of age than lambs from ewes receiving no Se (21.2 vs. 19.0 kg; P = 0.04) or lambs from ewes receiving Se-yeast at 4.9 mg Se/wk (19.2 kg; P = 0.09). This effect was more pronounced in ewes raising multiple lambs. We conclude that supranutritional supplementation of ewes with Se-yeast at 24.5 mg Se/wk improves lamb growth and ewe health without negatively affecting reproductive performance.

Organic and inorganic selenium: II. Transfer efficiency from ewes to lambs.

Adequate Se transfer from ewes to lambs is important to prevent Se-deficiency diseases. To evaluate how different chemical forms of Se administered at comparative dosages to mature ewes affect Se status of their lambs, 240 ewes were divided into 8 treatment groups (n = 30 each) and drenched weekly (at an amount equal to their summed daily intake) with no-Se (controls); at recommended amounts (4.9 mg of Se/wk) with inorganic Na-selenite, inorganic Na-selenate, or organic Se-yeast; or at supranutritional amounts (14.7 and 24.5 mg of Se/wk) with Na-selenite or Se-yeast for 1 yr. Weekly drenching of Se was effective at increasing (P < 0.002) Se concentrations in ewe colostrum and milk at 30 d of lactation and in improving (P < 0.001) the Se status of lambs (whole-blood and serum-Se concentrations at birth, and skeletal-muscle Se concentrations at 14 d of age). Selenium concentrations in lacteal secretions were greater in ewes drenched with Se-yeast (colostrum: 374, 436, and 982 ng/mL at 4.9, 14.7, and 24.5 mg of Se/wk, respectively; milk: 26, 39, 64 ng/mL) compared with ewes drenched with Na-selenite (colostrum: 204, 334, 428 ng/mL; milk: 16, 21, 24 ng/mL), and were also greater (P < 0.001) in their lambs. Selenium concentrations continued to increase (P < 0.001) in lamb whole blood (558 and 695 ng/mL at 14.7 and 24.5 mg of Se/wk, respectively), serum (126, 183 ng/mL), and skeletal muscle (991, 1,696 ng/mL) with supranutritional concentrations of Se-yeast, whereas Se concentrations did not differ in whole blood (304, 332 ng/mL), serum (77, 85 ng/mL), or skeletal muscle (442, 482 ng/mg) of lambs from ewes drenched with 14.7 or 24.5 mg of Se/wk of Na-selenite. We conclude that weekly oral drenching of ewes during gestation and lactation with organic Se-yeast results in a more efficient transfer of Se (over a wide range of supplementation rates) from ewe to lamb than does inorganic Na-selenite.

Organic and inorganic selenium: I. Oral bioavailability in ewes.

Although the essentiality of dietary Se for sheep has been known for decades, the chemical source and Se dosage for optimal health remain unclear. In the United States, the Food and Drug Administration (FDA) regulates Se supplementation, regardless of the source of Se, at 0.3 mg of Se/kg of diet (as fed), which is equivalent to 0.7 mg of Se/d or 4.9 mg of Se/wk per sheep. The objectives of this study were to evaluate the effects of Se source (inorganic vs. organic) and supplementation rate (FDA vs. supranutritional rates of 14.7 and 24.5 mg of Se/wk) on whole-blood (WB) and serum-Se concentrations. Mature ewes (n = 240) were randomly assigned to 8 treatment groups (n = 30 each) based on Se supplementation rate (4.9, 14.7, and 24.5 mg of Se•wk(-1)•sheep(-1)) and source [Na-selenite, Na-selenate (4.9 mg/wk only), and organic Se-yeast] with a no-Se control group (0 mg of Se/wk). Treatment groups were balanced for healthy and footrot-affected ewes. For 1 yr, ewes were individually dosed once weekly with 0, 4.9, 14.7, or 24.5 mg of Se, quantities equivalent to their summed daily supplementation rates. Serum- and WB-Se concentrations were measured every 3 mo in all ewes; additionally, WB-Se concentrations were measured once monthly in one-half of the ewes receiving 0 or 4.9 mg of Se/wk. Ewes receiving no Se showed a 78.8 and 58.8% decrease (P < 0.001) in WB- (250 to 53 ng/mL) and serum- (97 to 40 ng/mL) Se concentrations, respectively, over the duration of the study. Whole-blood Se decreased primarily during pregnancy (-57%; 258 to 111 ng/mL) and again during peak lactation (-44%; 109 to 61 ng/mL; P < 0.001). At 4.9 mg of Se/wk, Se-yeast (364 ng/mL, final Se concentration) was more effective than Na-selenite (269 ng/mL) at increasing WB-Se concentrations (P < 0.001). Supranutritional Se-yeast dosages increased WB-Se concentrations in a dose-dependent manner (563 ng/mL, 14.7 mg of Se/wk; 748 ng/mL, 24.5 mg of Se/wk; P < 0.001), whereas WB-Se concentrations were not different for the Na-selenite groups (350 ng/mL, 14.7 mg of Se/wk; 363 ng/mL, 24.5 mg of Se/wk) or the 4.9 mg of Se/wk Se-yeast group (364 ng/mL). In summary, the dose range whereby Se supplementation increased blood Se concentrations was more limited for inorganic Na-selenite than for organic Se-yeast. The smallest rate (FDA-recommended quantity) of organic Se supplementation was equally effective as supranutritional rates of Na-selenite supplementation in increasing WB-Se concentrations, demonstrating the greater oral bioavailability of organic Se.