As more and more women decide to become mothers later in life, the risk of experiencing pregnancy complications also increases. New research explores why this may be the case, suggesting that a delayed and longer labor may play a role.

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New research explains some of the mechanisms behind childbirth complications.

An increasing number of women are choosing to have their first child later in life. The Centers for Disease Control and Prevention (CDC) report that in the last 4 decades, the number of women choosing to have a child at the age of 35 or above has risen dramatically – from 1.7 per 1,000 births in 1973, to 11 per 1,000 in 2012.

Some studies suggest that the increase in first births to older mothers has also been accompanied by an increase in pregnancy complications.

An advanced maternal age is considered to be a factor in high-risk pregnancy, and older mothers are more likely to need a cesarean section in order to aid delivery. Some of the cases requiring assisted delivery suggest that there are issues with how well the uterus contracts during birth.

Researchers from King’s College London (KCL) in the United Kingdom have investigated the physiological changes in the mother’s body that could explain contraction-related pregnancy complications.

The study, published in the journal Physiology, used mouse models to examine the link between maternal aging and the structure of the uterus.

The researchers, led by Dr. Rachel M. Tribe, reader in women’s health at KCL, used a pregnant mouse model to mimic human maternal aging. Typically, the fertility of a female mouse peaks at 3-5 months old, so 8-month-old mice were considered equivalent to a human mother aged 35.

Tribe and team analyzed the physiological functions of the cervix and uterine muscles of the pregnant mice. They looked at how the contractions take place, how the uterus responds to oxytocin, and the number of mitochondria available, as well as the signaling of progesterone.

Oxytocin is a hormone produced naturally by our bodies. Among its many functions, oxytocin is also released during childbirth to facilitate the contractions. The hormone can also be administered as a drug to induce labor.

Mitochondria are the so-called powerhouse of the cell. They are small parts inside a cell and are responsible for producing energy. In this study, researchers examined mitochondria in order to see how much energy they provided for uterus muscle contractions.

Progesterone is a hormone known to play a crucial role in pregnancy. Apart from helping the uterus to thicken and get ready for embryo implantation, it also strengthens the pelvic walls in preparation for the contractions. It is also responsible for reducing uterine activity, thus keeping the uterus “calm” until term.

The researchers found alterations in hormonal signals and muscle structure that could explain the delayed onset of labor.

In older mice, the ability of the muscles to contract was impaired. The muscles were also less responsive to contraction-inducing oxytocin and had lower numbers of energy-producing mitochondria.

Researchers also found alterations in progesterone signaling, which they believe caused a delay in labor.

“Our research highlights that there are key physiological and cellular changes associated with a mother’s age that result in labor dysfunction. The timing of delivery and progress of labor is directly related to maternal age and this can cause complications during birth.”

Dr. Rachel M. Tribe

Dr. Rima Patel, research associate at the Division of Women’s Health at KCL and study co-author, also weighs in on the contribution of the study.

“Our study uses a mouse model so further research involving measuring hormones and analyzing uterus tissue in older pregnant women is now needed. Studies like this in maternal aging are essential to inform future clinical management strategies for older mothers to ensure more hassle-free and successful births.”

Learn how first-time birth in later life may increase longevity.