Heavy lifting during pregnancy has historically been met with universally cautious advice that discouraged high-intensity resistance training, exercising on your back, and the breath-holding technique known as the Valsalva maneuver.

This cautious approach, however, was built not on direct evidence of harm, but on an absence of evidence altogether. The recommendations stemmed from a logical fear that heavy exertion could compromise the health of the mother or fetus. For lifters, this often meant choosing between the activity they love and the prevailing medical advice.

Now, that is changing. A new wave of research is finally putting these long-held beliefs to the test.

By directly measuring maternal and fetal responses to heavy lifting, scientists are providing the first clear, data-driven answers to the pregnant athlete's dilemma.

What they are finding is challenging the notion that you should not heavy lifting during pregnancy.

It is important to note all studies focused on healthy, highly active individuals with significant prior experience in resistance training (a minimum of two years was a criterion in the experimental studies). The findings cannot be generalized to individuals who are new to resistance training or those with medical or obstetric contraindications to exercise.

‍Finding 1: Fetal Vitals Remain Stable, Even Under Heavy Loads

A primary concern has always been that the physical strain of heavy lifting could compromise blood flow or cause acute distress to the fetus. New research using direct fetal monitoring suggests this fear may be unfounded for healthy, trained individuals.

In a 2025 study in the British Journal of Sports Medicine, researchers monitored 10 experienced lifters (at least 2 years of experience) in their second and third trimesters (mean of 26.4 weeks gestation) as they performed heavy squats, deadlifts, and bench presses at intensities up to 90% of their 10-repetition maximum (10-RM). The results were striking: they observed no instances of fetal bradycardia (a dangerously slow heart rate), and the fetal heart rate did not change significantly from pre- to post-exercise.

These groundbreaking findings were reinforced by the largest study of its kind to date.

In another 2025 BMJ Journal study Pushing limits: the acute effects of a heavy-load resistance protocol and supine exercise on fetal well-being. They examined 48 pregnant athletes between 26 and 35 weeks of gestation during a heavy-load protocol. They also found that fetal heart rates remained within the normal range. The study noted only one transient case of bradycardia, which resolved on its own within three minutes. While not considered clinically significant, the protocol was stopped for that individual.

The researchers also found that while umbilical artery blood flow was unchanged, uterine artery blood flow—the circulation supplying the uterus—actually improved after the exercises (indicated by a decrease in the Pulsatility Index, a measure of blood flow resistance). This provides the first direct physiological evidence that a healthy fetus can tolerate the acute stress of its mother's heavy lifting session.

Finding 2: The 'Forbidden' Breath-Hold Appears Safe

The Valsalva maneuver, a breath-holding technique used to brace the core and stabilize the body during a heavy lift, has long been a major taboo in prenatal fitness. The theory was that the increase in intra-abdominal pressure could reduce the mother's cardiac output and, consequently, blood flow and oxygen to the fetus.

New laboratory evidence directly challenges this theory. The Moolyk et al. study specifically tested the Valsalva maneuver during sets performed at 90% of a 10-rep max and found no adverse fetal responses.

The researchers were so confident in their findings that they concluded:

“Our findings suggest that high-intensity resistance exercises are well tolerated by both mother and fetus, including while using the Valsalva manoeuvre.”

This lab-based finding is supported by survey data from a study: Impact of heavy resistance training on pregnancy and postpartum health outcomes which found that perinatal health outcomes were not different for pregnant lifters who used the Valsalva maneuver compared to those who avoided it.

Finding 3: The Bench Press May Not Be Off-Limits

It's one of the cardinal rules of prenatal fitness: once you hit the second trimester, the flat bench (supine position) is off-limits. The fear, rooted in the real phenomenon of "vena cava syndrome," is that the weight of the uterus can act like a clamp on a major vein, reducing blood return to the heart. This can cause dizziness in the mother and, theoretically, reduce blood flow to the fetus.

While the syndrome is real, recent research questions whether a blanket ban on all short-duration supine exercise is necessary for experienced lifters. The Moolyk et al. study included the supine barbell bench press in its protocol and found it was well tolerated by both mother and fetus, with no adverse events recorded. In the larger Dalhaug et al. study, which tested both flat and incline bench presses, only one of the 48 athletes reported feeling dizzy. Crucially, even in that instance, the fetus showed no signs of distress, and fetal blood flow was maintained.

For an experienced lifter performing a controlled set of a supine exercise, the risk appears to be very low and may not warrant a complete ban.

Finding 4: Maintaining Intensity Is Linked to Better Outcomes

Perhaps the most counter-intuitive finding is that for already-trained individuals, significantly reducing training intensity might not be the best approach. Beyond direct laboratory measurements, a large-scale survey by Prevett et al. of 679 women who performed heavy lifting during pregnancy (at least 80% of their one-rep max) provides real-world support for maintaining intensity. The study found that participants who maintained their pre-pregnancy training levels until delivery reported significantly fewer pregnancy and delivery complications than those who ceased or reduced their training.

This suggests that for athletes whose bodies are already adapted to high-intensity training, maintaining that stimulus may offer protective benefits. This is further supported by the Moolyk et al. lab study, which observed that the pregnant participants, well into their second and third trimesters, lifted weights similar to the non-pregnant control group. This confirms that maintaining high intensity is not just correlated with better outcomes, but is physiologically possible late into pregnancy.

The key takeaway is that for this population, deconditioning by drastically reducing intensity may be unnecessary.

A New Foundation for an Old Conversation

This new research provides a foundation of evidence to support what many female athletes have anecdotally known for years: their bodies, and their babies, are far more resilient than the old guidelines suggest.

It shows that for experienced lifters with healthy, uncomplicated pregnancies, continuing to lift heavy during pregnancy, using the Valsalva maneuver, and performing short-duration supine exercises appears to be safe.

This data doesn't just empower individual athletes to have more informed conversations with their doctors; it challenges the medical community to evolve its recommendations based on evidence, not just an absence of it. The evidence is mounting, and the conversation must now shift from what pregnant athletes can't do to how we can best support what their bodies are clearly capable of.

‍

‍

‍