fertility

#Age-sex-specific estimates of population and #fertility by GBD 2017

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  • The Lancet

Background

Population estimates underpin demographic and epidemiological research and are used to track progress on numerous international indicators of health and development. To date, internationally available estimates of population and fertility, although useful, have not been produced with transparent and replicable methods and do not use standardised estimates of mortality. We present single-calendar year and single-year of age estimates of fertility and population by sex with standardised and replicable methods.

Methods

We estimated population in 195 locations by single year of age and single calendar year from 1950 to 2017 with standardised and replicable methods. We based the estimates on the demographic balancing equation, with inputs of fertility, mortality, population, and migration data. Fertility data came from 7817 location-years of vital registration data, 429 surveys reporting complete birth histories, and 977 surveys and censuses reporting summary birth histories. We estimated age-specific fertility rates (ASFRs; the annual number of livebirths to women of a specified age group per 1000 women in that age group) by use of spatiotemporal Gaussian process regression and used the ASFRs to estimate total fertility rates (TFRs; the average number of children a woman would bear if she survived through the end of the reproductive age span [age 10–54 years] and experienced at each age a particular set of ASFRs observed in the year of interest). Because of sparse data, fertility at ages 10–14 years and 50–54 years was estimated from data on fertility in women aged 15–19 years and 45–49 years, through use of linear regression. Age-specific mortality data came from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 estimates. Data on population came from 1257 censuses and 761 population registry location-years and were adjusted for under enumeration and age misreporting with standard demographic methods. Migration was estimated with the GBD Bayesian demographic balancing model, after incorporating information about refugee migration into the model prior. Final population estimates used the cohort-component method of population projection, with inputs of fertility, mortality, and migration data. Population uncertainty was estimated by use of out-of-sample predictive validity testing. With these data, we estimated the trends in population by age and sex and in fertility by age between 1950 and 2017 in 195 countries and territories.

Findings

From 1950 to 2017, TFRs decreased by 49.4% (95% uncertainty interval [UI] 46.4–52.0). The TFR decreased from 4.7 livebirths (4.5–4.9) to 2.4 livebirths (2.2–2.5), and the ASFR of mothers aged 10–19 years decreased from 37 livebirths (34–40) to 22 livebirths (19–24) per 1000 women. Despite reductions in the TFR, the global population has been increasing by an average of 83.8 million people per year since 1985. The global population increased by 197.2% (193.3–200.8) since 1950, from 2.6 billion (2.5–2.6) to 7.6 billion (7.4–7.9) people in 2017; much of this increase was in the proportion of the global population in south Asia and sub-Saharan Africa. The global annual rate of population growth increased between 1950 and 1964, when it peaked at 2.0%; this rate then remained nearly constant until 1970 and then decreased to 1.1% in 2017. Population growth rates in the southeast Asia, east Asia, and Oceania GBD super-region decreased from 2.5% in 1963 to 0.7% in 2017, whereas in sub-Saharan Africa, population growth rates were almost at the highest reported levels ever in 2017, when they were at 2.7%. The global average age increased from 26.6 years in 1950 to 32.1 years in 2017, and the proportion of the population that is of working age (age 15–64 years) increased from 59.9% to 65.3%. At the national level, the TFR decreased in all countries and territories between 1950 and 2017; in 2017, TFRs ranged from a low of 1.0 livebirths (95% UI 0.9–1.2) in Cyprus to a high of 7.1 livebirths (6.8–7.4) in Niger. The TFR under age 25 years (TFU25; number of livebirths expected by age 25 years for a hypothetical woman who survived the age group and was exposed to current ASFRs) in 2017 ranged from 0.08 livebirths (0.07–0.09) in South Korea to 2.4 livebirths (2.2–2.6) in Niger, and the TFR over age 30 years (TFO30; number of livebirths expected for a hypothetical woman ageing from 30 to 54 years who survived the age group and was exposed to current ASFRs) ranged from a low of 0.3 livebirths (0.3–0.4) in Puerto Rico to a high of 3.1 livebirths (3.0–3.2) in Niger. TFO30 was higher than TFU25 in 145 countries and territories in 2017. 33 countries had a negative population growth rate from 2010 to 2017, most of which were located in central, eastern, and western Europe, whereas population growth rates of more than 2.0% were seen in 33 of 46 countries in sub-Saharan Africa. In 2017, less than 65% of the national population was of working age in 12 of 34 high-income countries, and less than 50% of the national population was of working age in Mali, Chad, and Niger.

Interpretation

Population trends create demographic dividends and headwinds (ie, economic benefits and detriments) that affect national economies and determine national planning needs. Although TFRs are decreasing, the global population continues to grow as mortality declines, with diverse patterns at the national level and across age groups. To our knowledge, this is the first study to provide transparent and replicable estimates of population and fertility, which can be used to inform decision making and to monitor progress.

Funding

Bill & Melinda Gates Foundation.

Depression may impair fertility

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Study: Severely depressed women have a lower chance of becoming pregnant. Medication does not appear to be the cause.

Severe depression seems to impair fertility – regardless of treatment with psychotropic medication. This is the outcome of a study carried out by US researchers published in the “American Journal of Obstetrics & Gynecology”.

More than 2,100 women aged between 21 and 45 years who planned to become pregnant participated in the study carried out by researchers at Boston University (Massachusetts). The scientists examined factors that may impair fertility. Participants were asked to report their current depressive symptoms and use of psychotropic medications. Of these women, 22 per cent reported to have been clinically diagnosed with depression at some point in their medical history. 17.2 per cent were former users of psychotropic medications, and 10.3 per cent were current users of these medications.

According to the results, women with severe depressive symptoms were 38 per cent less likely to become pregnant in a normal menstrual cycle compared to participants with no or low symptoms of depression. It made no difference whether or not those affected had taken psychotropic medications.

In addition, the results showed that taking benzodiazepines led to a decrease in fertility. In contrast, earlier treatment with SSRIs (selective serotonin reuptake inhibitors) increased the chance of conception. However, absolute numbers of those affected were too small; further trials are therefore needed.

The underlying reasons for the association between depression and fertility are still unknown. There are several potential mechanisms, but they still need to be studied further. This includes the fact that depression has been associated with dysregulation of the hypothalamic-pituitary-adrenal axis, which may have an impact on the menstrual cycle and impair fertility.

Asthma may impair fertility

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Asthmatics have a lower pregnancy rate and take longer to get pregnant.

Asthma is evidently associated with reduced fertility in women. A Danish study, published in the “European Respiratory Journal” shows that asthmatics have a lower birth rate and an increased time to pregnancy.

Researchers from the University of Copenhagen examined 245 women aged between 23 and 45 years with unexplained fertility problems who were undergoing fertility treatment. All participants were tested for asthma and allergies and were followed for at least 12 months. Ninety-six participants were diagnosed with asthma.

Findings showed that the average time for women with asthma to get pregnant was significantly longer. Participants without asthma needed an average of 32.2 months to pregnancy while those with asthma needed 55.6 months. Additionally, women with asthma were less likely to get pregnant – 39.6 per cent achieved pregnancy by the end of the study, compared with 60.4 per cent of healthy women. The older a woman with asthma is, the more pronounced the link between fertility problems and asthma.

“We do not yet now the causal relationship”, study author Elisabeth Juul Gade noted with regret. It could be a complex association in which the type of asthma, the patient’s well-being, asthma medication and hormones play a role. Given the results, doctors should advise women with asthma to optimise their treatment and to become pregnant at an earlier age.