This Week in Sex is a weekly summary of news and research related to sexual behavior, sexuality education, contraception, STIs, and more.

Study: New Maternal Tests Are Accurate

Last fall, Rewire reported on a new, non-invasive prenatal test that could detect chromosomal anomalies in a fetus during the early stages of a pregnancy using the mother’s blood. Marketed under the brand names MaterniT21, Harmony, verifi, and Panorama, the screening measure is called cfDNA testing (or cell-free fetal DNA testing). Fragments of fetal DNA—which makes up between 3 and 13 percent of the pregnant person’s blood during pregnancy but disappears entirely right after delivery—are isolated through a simple blood draw from the mother and checked for abnormalities, including Down syndrome, Edward syndrome, and Patau syndrome, all of which can cause serious developmental and medical issues. As an added bonus, the test, which can be given as early as nine weeks into a pregnancy, can reveal the fetus’ gender.

The test is seen as more accurate than the currently used method, in which physicians take measurements of a fetus’ neck during an ultrasound and results of blood tests on the mother to calculate the probability of chromosomal abnormalities. Women who are not comforted by these results can then choose to have amniocentesis or chorionic villus sampling, which use cells from the amniotic fluid or the placenta respectively and can give definitive answers. These tests, however, are invasive and carry a small risk of miscarriage. Moreover, they cannot be done until later in pregnancy.

The new tests could mean more definitive answers, earlier, without risks. Thus far, however, the testing has been used mainly with women declared high-risk because of their advanced age, issues with a prior pregnancy, or other health problems.

A new study, which was sponsored by the manufacturer of one of the cfDNA brands and published in the New England Journal of Medicine, is the first to look at the use of this screening method in a general population. Researchers looked at results from nearly 2,000 women who had both the standard combined screening and the cfDNA test. Both the old and new tests found eight chromosomal abnormalities among the pregnancies screened, of which five were cases of Down syndrome. The cfDNA tests, however, were much less likely to return a false positive than the older test (0.3 percent versus 3.6 percent).

Experts seem to think this is a good result but not necessarily enough to change practice standards and start using cfDNA tests on all pregnant women. Some note that for the purposes of this study, the cfDNA testing was done later in pregnancy than it would normally be conducted, and that additional studies need to confirm that it’s accurate at early stages. Others also point out that the cost of the new tests may be prohibitive—they run between for $1,200 and $2,700, compared to $500 to $700 for the previous generation of testing. Nonetheless, in their editorial accompanying the study, the editors of the New England Journal of Medicine say that DNA tests are part of a new, fundamentally different era of prenatal testing. Still, it may take a while before this test is offered to every pregnant person.

Older Fathers Linked to Psychiatric Issues in Children

We have known for a long time that advanced maternal age is linked to various health issues in children, including Down syndrome and other chromosomal abnormalities. Now there’s growing evidence that the father’s age may be important as well.

A new study analyzed all births in Sweden between 1973 and 2001 (about two million) and found that children born to fathers who were age 45 or older were 13 times more likely to have attention deficit hyperactivity disorder (ADHD), 25 times more likely to have bipolar disorder, and more than twice as likely to have autism, psychotic disorders, and substance abuse problems as well as to attempt suicide than those born to younger fathers. They were also almost twice as likely to fail a grade or drop out of school. Moreover, the risk went up as the father’s age went up.

While it is tempting to pin this on a decrease in sperm quality, which is known to happen as men age, the study does not try to explain what causes the link. Other factors, such as family structure and environment, may play a role as well.

This research, published in JAMA Psychiatry, is important as people in the United States and elsewhere are putting off childbearing until later ages.

C-Section Linked to Weight

A new study, published in the online journal PLOS ONE, examined data from 15 studies that included more than 38,000 participants. Researchers compared the body mass index of adults born via c-section to that of those born through vaginal delivery. They found that those born via c-section were 26 percent more likely to be overweight and 22 percent more likely to be obese as adults compared to those born through vaginal delivery.

Though the study did not try to determine the cause of this correlation, Dr. Matthew Hyde, one of the researchers, explained in a press release, “There are plausible mechanisms by which cesarean delivery might influence later body weight. The types of healthy bacteria in the gut differ in babies born by cesarean and vaginal delivery, which can have broad effects on health. Also, the compression of the baby during vaginal birth appears to influence which genes are switched on, and this could have a long-term effect on metabolism.”

In fact, this is not the first study to suggest a link between c-sections and obesity later in life. Previous studies have also suggested that babies born via c-section may have higher rates of diabetes and asthma. Additional research is necessary to determine if the c-section itself, or some other factor, causes these health issues.