Should You Avoid Crunches During Pregnancy?

There seems to be no greater time of uncertainty about health than during pregnancy. We hear polarizing opinions about what is safe for baby and mother across all sorts of domains of health; from what you should eat, what you should do for activity, how you should sleep, the list goes on. As primary care workers, we physiotherapists, chiropractors and massage therapists often end up hearing about our being asked on our stance on these subjects.

One such question recently came up regarding the safety of sit-ups during pregnancy. During an examination with a woman in her second trimester, I asked the patient to get up from lying to sitting. To my surprise, this healthy and fit individual slowly and methodically moved through a series of maneuvers before cautiously sitting upright. When I asked her about why she got up this way, she told me this was the way her doctor had taught her to get up to avoid doing a sit-up. While I am not a specialist in peripartum patients (pregnancy and post-pregnancy), I am familiar enough with the current guidelines for activity to know this seemed wrong. And so began a dig into the current research.

UNDERSTANDING abdominal muscle ANATOMY

Before we go into the weeds of research and recommendations, we should begin with a foundational understanding of anatomy and what happens to the abdomen during pregnancy.

Often referred to as “your core” are your abdominal muscles. These are the muscles in the front between your ribs and pelvis that allow you to crunch, exhale quickly and help to keep your spine stable. The most distinctive muscle here is your rectus abdominus. This is the “6-pack muscles” we often work so hard to show off (yes, we all have them, in most people they are just covered by a thicker layer of fat). Technically, the rectus abdominus is one muscle that has distinctive separations created by the linea alba, which is a type of connective tissue to add further strength and support to the abdominal wall.

WHAT CHANGES IN your anatomy during PREGNANCY?

During pregnancy, the body undergoes a remarkable set of anatomical transformations to accommodate and nurture fetal growth, and among the most notable are changes to the rectus abdominis muscle and the surrounding linea alba.

As the uterus expands to support the developing fetus, the rectus abdominis on both sides must curve outward to brace the growing belly, a mechanical adaptation driven by the increased intra-abdominal pressure and the need to maintain core stability. This progressive reshaping places new demands on the abdominal wall, and over time, the constant stretching and altered tension contribute to weakening of the muscle tissue and widening of the linea alba, that fibrous seam that runs down the midline of the abdomen.

The cumulative effect of these changes leads to visual widening between the abdominal muscles. If the distance between the abdominal muscles (also known as the inter-recti distance, or IRD) gets big enough, we diagnose the patient as having diastasis recti abdominis (DRA).

Beyond seeing spacing between the ab muscles, the other notable symptom of DRA is what is called coning. Coning refers to a visible or palpable bulge that emerges along the midline of the abdomen when abdominal pressure is increased (for example, during a sit-up, pushing, coughing, or specific abdominal exercises). Rather than the abdomen bulging uniformly, the weakened linea alba and separated rectus muscles allow a localized projection or “cone-like” shape to form centrally under strain. It sounds scary to hear that part of your abdomen is protruding, but know that it isn’t a hole in your abdomen, there is still the linea alba protecting overtop, it’s just that the linea alba is thinner and more stretchy over this area.

If the distance between the abdominal muscles (also known as the inter-recti distance, or IRD) gets big enough, we diagnose the patient as having diastasis recti abdominis (DRA).

IS DIASTASIS RECTI ABDOMINIS A PROBLEM?

And here lies one of the first myths we need to bust. Diastasis recti abdominis DRA is a common and expected part of pregnancy. As we discussed, as the baby grows, the body needs to make space to accommodate. I equate this to blowing up a balloon, as the pressure builds, something is going to have to stretch, and in humans, this invariably leads to stretching of the linea alba. To put this into perspective, here are the results of a few studies[1]:

33% at the 21st week of gestation

Nearly 100% at 35 weeks of gestation[2]

60% at 6 weeks post partum

33% at one year post partum

The big takeaway here is that we shouldn’t stigmatize diastasis recti during and after pregnancy; it is completely normal (arguably, it would be more amazing to see it not stretch!). The problem around this conversation is that the idea of our abdominal wall stretching apart sounds really scary, and that perhaps we should avoid activities that risk stretching the abdominal wall further. This ill-founded belief lies at the heart of the well-intended advice given to my patient.

DOES EXERCISE LEAD TO DIASTASIS RECTI ABDOMINIS?

Traditional advice to avoid sit-ups or curl-ups in pregnancy was based on concerns that these exercises raise intra-abdominal pressure and might stretch the midline more. That would make sense if we assumed that the body, and more specifically the linea alba, was like an inner rubber band and stretched over time rather than being an adaptable organism. As such, these older theoretical models should be tested, and newer evidence has come out to challenge the previous blanket restrictions on rectus abdominis (RA) work.

A recent high-quality study (three-arm randomized controlled trial) directly compared general prenatal exercise without an abdominal focus (control) to the same program plus transversus abdominis (TrA) “drawing-in” exercises (think core activation stuff like a plank or dead-bug), and to the same program plus rectus abdominis–targeted crunch-style exercises[3]. After 12 weeks, all groups showed a similar increase in inter-recti distance (IRD) across pregnancy. As a woman progresses through pregnancy, we should, of course, expect the IRD to increase a bit, what is great to see is that the crunch group didn’t make the IRD any larger compared to the other groups! There were also no meaningful between-group differences in pelvic floor dysfunction symptoms. The practical takeaway is that adding either ab exercises, be it gentler/stability exercises like deadbug or more rectus abdominis exercises like a sit-up up did not substantially change IRD compared with general exercise, suggesting that pregnant people do not need to avoid targeted ab exercises to prevent IRD.

In fact, it has been suggested that interventions focused on physical activity may help maintain abdominal muscle tone, strength, and control, potentially offering a protective effect against the development of diastasis recti[4]. However, current evidence remains insufficient to confirm this hypothesis.

Pregnant people do not need to avoid targeted ab exercises to prevent IRD.

Is exercise safe for the BABY?

The short answer, based on recent research, is yes. Across the sessions, the amount of weight lifted and the rate of perceived exertion were similar for pregnant and non-pregnant participants, suggesting that pregnant individuals can engage in resistance-style movement without adding undue strain[5]. During activity, fetal safety appeared reassuring: there was minimal impact on fetal circulation or fetal heart rate. Umbilical blood flow metrics, such as the resistance index, remained within normal ranges across squats, bench presses, and deadlifts, indicating stable placental perfusion during these activities. Taken together, these findings support the notion that, with appropriate supervision and sensible programming, moderate resistance training can be compatible with a healthy pregnancy and does not appear to adversely affect fetal heart rate or umbilical blood. As always, individual risk factors and medical guidance should inform exercise decisions.

CONCLUSIONS

As we have reviewed, exercise and specifically crunches is safe for both mom and the baby. While crunches do place stress on the abdominal muscles and the linea alba, this doesn’t lead to permanent stretching or increased risk for diastasis recti. Speaking of which, diastasis recti shouldn’t necessarily be considered pathological but rather a normal part of the pregnancy process.

If you are concerned about what is safe during pregnancy, our team is happy to chat with you. Our goal is to keep you as healthy as possible through and beyond pregnancy.

REFERENCES

[1] Sperstad JB, Tennfjord MK, Hilde G, Ellström-Engh M, Bø K. Diastasis recti abdominis during pregnancy and 12 months after childbirth: prevalence, risk factors and report of lumbopelvic pain. Br J Sports Med. 2016;50(17):1092-1096. doi:10.1136/bjsports-2016-096065

[2] Fernandes da Mota PG, Pascoal AG, Carita AI, Bø K. Prevalence and risk factors of diastasis recti abdominis from late pregnancy to 6 months postpartum, and relationship with lumbo-pelvic pain. Man Ther. 2015;20(1):200-205. doi:10.1016/j.math.2014.09.002

[3] Cabral AL, Diniz ALD, Oliveira EH, et al. Transversus abdominis and rectus abdominis activation exercises do not alter inter-recti distance in pregnant women: a randomised trial. J Physiother. 2025;71(4):254-259. doi:10.1016/j.jphys.2025.09.013

[4] Benjamin DR, van de Water AT, Peiris CL. Effects of exercise on diastasis of the rectus abdominis muscle in the antenatal and postnatal periods: a systematic review. Physiotherapy. 2014;100(1):1-8. doi:10.1016/j.physio.2013.08.005

[5] Moolyk AN, Wilson MK, Matenchuk BA, et al. Maternal and fetal responses to acute high-intensity resistance exercise during pregnancy. Br J Sports Med. 2025;59(3):159-166. Published 2025 Feb 3. doi:10.1136/bjsports-2024-108804