Love Hormone: Oxytocin Can Halt Pregnancy, Says Animal Study

Oxytocin and Its Role in Halting Early Pregnancies

A study on lab animals, specifically mice, reveals that the "cuddle hormone" oxytocin, known for its role in bonding, also plays a crucial role in delaying early pregnancies.

According to recent research, oxytocin can induce a hibernation-like state in embryos at the earliest stages of development. This process, known as "diapause," allows a mother mouse to postpone pregnancy when resources are limited, such as when she is still nursing a previous litter.

What Is Diapause?

Embryonic diapause is a reversible suspension of pre-implantation embryo development.

This phenomenon occurs naturally in around 130 species, including mice, bats, and marsupials like kangaroos and possums.

Studying human pregnancies is particularly challenging. However, rare reports from in vitro fertilization (IVF) clinics suggest that some embryos, once placed in the uterus, may remain dormant for weeks before implanting. This indicates that a similar process might occur in humans.

Little is known about how embryos enter this state of arrested development or how long diapause can last.

Insights from the Study

Minder, the study’s first author and a graduate student at NYU Grossman School of Medicine, was eager to explore the link between oxytocin and diapause.

Oxytocin plays a critical role in both nursing and embryonic development in humans and other mammals.

The researchers began their study by placing male mice in cages with recently delivered female mice, allowing them to mate while the females were still nursing. They found that the next pregnancies in nursing mice lasted nearly a week longer than in non-nursing mice.

Further, the study revealed that oxytocin did more than just delay pregnancy—higher levels of the hormone caused most mice to lose their pregnancies entirely. The oxytocin levels observed during breastfeeding were significant enough to disrupt pregnancy.

To verify oxytocin's role in delaying implantation, the researchers administered a single dose of oxytocin (either 1 microgram or 10 micrograms) to mouse embryos in the lab. Even at these small doses, implantation in the uterus was delayed by up to three days.

These findings were published on March 5 in Science Advances in a special issue on women’s health.

Why Does Pregnancy Halt?

To further investigate, the researchers used optogenetics—a technique that activates specific neurons with light—to stimulate oxytocin release in pregnant mice. This allowed them to mimic the natural oxytocin pulses seen during nursing.

After five days of treatment, the scientists examined the mice's uteruses and found that embryos in five out of six mice had entered diapause, indicating that oxytocin had paused their development.

In contrast, pregnant mice that did not receive oxytocin stimulation showed no signs of diapause.

In another experiment, the team treated early mouse embryos in lab plates with oxytocin. This also caused cellular changes consistent with diapause.

The study also found that diapause occurred even in embryos lacking oxytocin receptors, suggesting that multiple signals might trigger the pause. Additionally, oxytocin appears to be essential for embryos to survive this arrested state.

According to Dr. Froemke, the next step is to explore how diapause reverses and allows cell development to resume. The researchers also plan to study how diapause affects the health and development of offspring and its potential implications in reproductive medicine.

While these findings are promising, Dr. Froemke cautions that despite similarities between humans and mice, their reproductive systems differ significantly.

"Our findings suggest that oxytocin provides an evolutionarily conserved strategy for successful reproduction by synchronizing embryonic growth with uterine development during pregnancy. However, this study did not examine the role of other pregnancy-related hormones, such as progesterone and estrogen, in diapause."

Reference:

1. Minder, Jessica L., Sarah B. Winokur, Janaye Stephens, Jie Tong, Naomi L. Cassel, Luisa Schuster, Habon A. Issa et al. "Oxytocin Induces Embryonic Diapause." Science Advances, (2025). Accessed March 29, 2025. https://doi.org/adt1763.

(Input from various sources)

(Rehash/Dr. Lakshmisahithi Tanneru/MSM)