As per the latest 2014 report by the US Centers for Disease Control and Prevention (CDC), twin birth rates hit all time high in 2014 in the United States. In 2014, the study reported 33.9 sets of twins per 1,000 births compared to 33.7 in 2013. It has been reported that mothers continued to get older in 2014 with the average age for the first-time mother has now become 26.3, which it was 26 in 2013. Despite of increase in twin birth rates, researchers reported 9% drop in birth rates in the United States in 2014 alone with some states showed more than 50% drop since 2007. The drop in the birth rates has been due to improved efforts to educate teens and provide them long-term birth control like IUDs. The study found increase in the birth rate for women in their 30s, 40s and even 50s over the years to varying degrees.
Officials reported that increase in twin births is higher among older moms because the bodies of aged women tend to produce higher quantities of hormone that triggers the maturation of an egg-producing follicle. It further means a woman is more likely to have two eggs available for fertilization during a single cycle in her 30s than she is during her 20s. Though, it is not always that women in later age will have fraternal twins as older eggs are more likely to be unviable, a significant portion of them can be expected to have fraternal twins. Since 1980, about double increase in the twinning rate has been reported till now, which the rate was 18.9 twins per 1,000 births. According to the report, the birth rates of triplets and higher-order births declined in 2014, from 119.5 per 100,000 in 2013 to 113.5 per 100,000 in 2014, the lowest rate in 20 years and down more than 40% from the peak in 1998, when the birth rate of triplets and higher-order births reached a record 193.5 per 100,000.
It is also the fact that women at older age tend to follow the path of IVF, which can cause sharp increase in the number of births with three babies or more. As per the 2013 statistical report, more than 33% of the US twins and three-quarters of triplets were born with IVF. As per recent scenario, triplet (and higher) births are at a 20-year record low, even as twins continue to rise.