Pregnancy later in life may improve cognition in old age

Pregnancy causes many hormonal changes, with some research suggesting it may even impact some of the brain's functions. A new study suggests there may be cognitive advantages to having a pregnancy later in life.

Pregnancy normally increases the levels of some hormones in the mother's body, such as estrogen, progesterone, oxytocin, prolactin, cortisol, and some endorphins.

Some studies have linked higher levels of estradiol and cortisol with lower attention and have suggested mothers may have poorer verbal memory during pregnancy.

Negative emotional states have also been reported during pregnancy. In fact, 1 in 9 women experience depression before, during, or after pregnancy, according to the Centers for Disease Control and Prevention (CDC).

However, in the long run, pregnancy hormones may lead to better cognition and memory. A new study investigates the link between age at last pregnancy and a mother's cognitive abilities later in life.

Assessing the link between reproductive history and cognition

Researchers at the University of Southern California examined the association between reproductive history, hormonal exposure, and cognition in postmenopausal women.

Factors that influence hormonal exposure and that were considered by the study included reproductive period, pregnancy, and use of hormonal contraceptives.

The analysis evaluated a total of 830 women, using data from two clinical trials.

The average age of the participants was 60 years. The researchers made the necessary adjustments for age, race and ethnicity, income, and education.

Participants were evaluated using a variety of cognitive tests and a reproductive history questionnaire. Researchers tested participants' verbal memory by asking them to remember a list of words or to retell a story after being distracted.

They also assessed their psychomotor speed, attention span, and concentration, as well as their planning abilities, visual perception, and episodic memory.

Pregnancy after 35 linked to better cognition

The study revealed several associations, some of which have been supported by previous research, while others were more surprising.

The study found that postmenopausal women who had their last pregnancy after the age of 35 had better verbal memory.

Those who had their first pregnancy when they were 24 or older had significantly better executive function. This includes attention control, working memory, reasoning, and problem solving.

The study also revealed that having the first menstrual cycle at an early age, along with a longer reproductive life, also led to better executive function in later life.

Estrogen has been shown in previous studies to impact positively on the brain's chemistry, function, and structure in animal studies, explains lead author Roksana Karim, assistant professor of clinical preventive medicine at University of Southern California's Keck School of Medicine. Progesterone has been associated with brain growth and development of brain tissue, she adds.

"Starting your period early means you have higher levels of the female sex hormone being produced by the ovaries. Girls are receiving the optimal levels early, so it's possible that their brain structures are better developed compared to those who are exposed to estrogen levels associated with menstrual cycles at a later age."

Roksana Karim

Researchers also found that women who had used contraceptives for 10 years or more had better verbal memory and critical thinking skills.

"Oral contraceptives maintain and sustain a stable level of sex hormones in our bloodstream," Karim says. "Stable is good."

One result that surprised the researchers was the positive effect an incomplete pregnancy seemed to have on cognitive function.

Women who did not carry their pregnancy to term had better cognition, verbal memory, and executive function, compared with women who had only one full-term pregnancy.

"The finding that even incomplete pregnancies are beneficial was novel and surprising," says senior author Wendy Mack, professor of preventive medicine at the Keck School of Medicine.

Parity was also found to associate positively with cognition. Women who gave birth to two children had better cognition in older age, compared with mothers of one child.

Results at odds with some previous research

This is the first time a study has investigated the association between age at last pregnancy and cognitive function in older age, Karim says. Having the last baby at a later age can be an indicator of a later surge in pregnancy hormones, the author explains.

"Based on the findings, we would certainly not recommend that women wait until they're 35 to close their family, but the study provides strong evidence that there is a positive association between later age at last pregnancy and late-life cognition."

Roksana Karim

However, previous studies have shown that pregnancy can have a negative effect on brain function. Some researchers have found that pregnant women have worse verbal memory and word-listing learning skills, as well as poorer fluency when compared with women who are not pregnant.

Mack explains that such results may have been influenced by other factors, such as other bodily changes or environmental stressors.

"The issue is the human studies have not followed women for the long term. They just looked at women during pregnancy." she says. "We are not sure if we can expect to detect a positive estrogen effect at that point, as the many bodily changes and psychosocial stressors during pregnancy also can impact women's cognitive and emotional functions."

Overall, the new findings are both "intriguing and are supported by other clinical studies and animal studies," adds Mack.

                                      Having a pregnancy later in life may improve cognition in older age.