Pregnancy research, explained
What the studies behind common advice actually found
Last updated
Each summary below describes one study or review in plain language: who was studied, what changed, and what it does and does not show. Where a product on this site cites a study, this is the study.
New · 18 October 2026
2026 research update: dates, birthing balls and perineal massageWhat this year's studies found, how strong the evidence is, and where it falls short.New · 26 October 2026
Natural ways to bring on labour: what the research says (2026)Membrane sweeps, dates, sex, walking, castor oil and the rest, graded by evidence strength with safety notes.Date Fruit and Labor
Al-Kuran 2011 trial · 114 women (69 ate dates, 45 did not)
Women who ate 6 dates daily for 4 weeks before their due date arrived at the hospital more dilated (3.5cm vs 2cm), were more likely to go into labor naturally (96% vs 79%), and had shorter early labor (8.5 hours vs 15 hours). The study suggests dates may help your body prepare for labor.
Bottom line: In one 2011 observational study, eating dates daily from 36 weeks was linked to more spontaneous labour and a shorter early labour. Later reviews rate the evidence low to moderate.
Perineal Massage and Tearing
2022 Meta-analysis (16 trials, 6,487 women) · 6,487 women across 16 randomized trials
Massaging the perineum (the area between the vagina and rectum) from 34 weeks was linked to 44% fewer severe tears during birth in this pooled analysis. It also reduced the need for episiotomy (a surgical cut) and pain at 3 months postpartum. Minor tears were not affected.
Bottom line: In a 2022 meta-analysis of 16 trials, perineal massage from 34 weeks, 3 to 4 times a week, was linked to fewer severe tears and fewer episiotomies.
Birthing Ball and Labor Outcomes
2025 Meta-analysis (10 trials, 1,008 women) · 1,008 women across 10 randomized trials
In a 2025 meta-analysis of 10 trials, using a birthing ball during labor was linked to about 45% fewer caesareans in relative terms, pain scores about 20% lower, and a first stage of labor more than 2 hours shorter. The trials were small and the certainty of the evidence is moderate to low.
Bottom line: In labour trials, using a birthing ball was linked to lower pain scores and fewer caesareans. The certainty of the evidence is moderate to low.
Colostrum Harvesting Before Birth
DAME Trial (Lancet 2017) · 635 women with diabetes in pregnancy (randomized controlled trial)
The DAME trial found that expressing colostrum twice daily from 36 weeks is safe for low-risk pregnancies. Babies whose mothers harvested colostrum were more likely to be exclusively breastfed during their hospital stay. Having colostrum stored can help avoid formula use if baby needs supplementation, and the practice may increase breastfeeding confidence.
Bottom line: Colostrum harvesting from 36 weeks is safe and increases exclusive breastfeeding in hospital.
White Noise and Infant Sleep
Spencer 1990 trial · 40 newborns (2-7 days old)
In this study, 80% of newborns fell asleep within 5 minutes when exposed to white noise, compared to only 25% who fell asleep on their own. White noise mimics the whooshing sounds babies hear in the womb.
Bottom line: In one small 1990 trial, 80% of newborns fell asleep within 5 minutes with white noise, against 25% without.
Prenatal Vitamins and Pregnancy Health
Cochrane Reviews & Evidence-based Recommendations (200+ studies) · Systematic review of 40+ trials
Iron supplementation reduces maternal anemia by 70%. Folic acid taken before conception and in early pregnancy reduces neural tube defects (like spina bifida) by up to 70%. Vitamin D (2000-4000 IU/day) is linked to lower risks of preeclampsia and preterm birth.
Bottom line: Iron and folic acid supplements in pregnancy reduce maternal anaemia and neural tube defects in large reviews.
Safe Sleep and SIDS Prevention
AAP 2022 Policy Statement · AAP Task Force on SIDS (systematic evidence review)
Always place babies on their back to sleep. This alone has reduced SIDS by 74% since 1990. Use a firm, flat surface with no loose bedding, pillows, or toys. Sleep sacks are safer than blankets. Room-sharing (but not bed-sharing) is recommended for the first 6 months.
Bottom line: Back sleeping on a firm surface with no loose bedding has cut SIDS deaths by 74%.
Baby Monitors and SIDS
AAP 2022 & JAMA 2018 · AAP expert panel + accuracy study of consumer monitors
Consumer baby monitors that claim to track vital signs are NOT recommended for SIDS prevention. Studies show they don't accurately measure oxygen levels or heart rate, and can give false reassurance or false alarms. Safe sleep practices are what actually prevent SIDS.
Bottom line: Do not rely on monitors to prevent SIDS. Safe sleep practices are what reduce the risk.
Caffeine and Pregnancy
Weng 2008 (Am J Obstet Gynecol) + ACOG Guidelines · 1,063 pregnant women (Kaiser Permanente)
This study found that 200mg+/day of caffeine doubled miscarriage risk compared to none. However, nausea in healthy pregnancies makes women avoid coffee, confounding results. A 2015 Cochrane review found insufficient evidence to confirm or refute effects. ACOG concludes moderate caffeine (<200mg/day) is likely safe, though some women prefer to avoid it entirely.
Bottom line: ACOG considers up to 200mg caffeine/day (about 2 cups) acceptable, but evidence is mixed.
Epidural Pain Relief
Anim-Somuah 2018 Cochrane Review · 11,000+ women across 52 randomized trials
Epidurals provide excellent pain relief, better than any other method. They slightly increase the chance of needing forceps or vacuum assistance but do NOT increase cesarean rates. They may slow the second stage of labor by about 15 minutes. There's no evidence of long-term effects on babies.
Bottom line: Epidurals provide the best pain relief with no increase in cesarean rates.
Exercise During Pregnancy
ACOG Committee Opinion 804 · ACOG expert committee (evidence-based recommendations)
Exercise during pregnancy is safe and beneficial for most women. It reduces risk of gestational diabetes, preeclampsia, and cesarean delivery. It also helps with mood and sleep. Unless you have specific complications, aim for 150 minutes of moderate activity per week. Your heart rate can go above 140; that old rule is no longer part of the guidance.
Bottom line: Exercise in pregnancy is safe and beneficial for most women. ACOG no longer uses the old 140 bpm heart-rate limit.
Sleep Training (Cry It Out)
Gradisar 2016 randomized trial (Pediatrics) · 43 infants aged 6-16 months
This randomized trial compared graduated extinction ('cry it out' with checks), bedtime fading, and a control group. Both sleep training methods reduced infant wake time and cortisol (stress hormone) levels. No differences in infant-parent attachment or behavioral problems at 12-month follow-up. A 2012 Australian trial (326 families) found no negative effects at age 6.
Bottom line: Randomized trials show sleep training works, reduces infant stress hormones, and has no long-term harm.
Breastfeeding Benefits
PROBIT trial (Kramer 2001) + Colen 2014 sibling study · 17,046 mother-infant pairs (PROBIT); 8,237 children (sibling study)
The PROBIT trial (Belarus, randomized) found breastfeeding reduced gastrointestinal infections and eczema in the first year, but 6.5-year follow-up showed no IQ difference. The Colen sibling study compared siblings where one was breastfed and one wasn't. Within the same family, most claimed benefits (obesity, asthma, hyperactivity, IQ) disappeared, suggesting confounding by family factors.
Bottom line: Proven benefits: fewer GI infections and eczema in year one. Long-term IQ/obesity claims are confounded.
Bed Rest During Pregnancy
Sosa 2015 Cochrane Review · Systematic review (1,266 women in analyzed trial)
Despite being commonly prescribed, there's no evidence that bed rest helps prevent or treat any pregnancy complication: not preterm labor, not preeclampsia, not placenta previa. It can actually cause harm: muscle atrophy, blood clots, bone loss, and psychological effects like depression. Yet many women are still put on bed rest.
Bottom line: Bed rest is not supported by evidence and may cause harm.
Amniocentesis and CVS Safety
Salomon 2019 meta-analysis (Ultrasound Obstet Gynecol) · Meta-analysis of 12 amnio + 7 CVS controlled studies
This 2019 meta-analysis found the procedure-related miscarriage risk is much lower than the commonly cited 1-in-200. For amniocentesis, the added risk is approximately 0.30% (1 in 333). For CVS, it's about 0.20% (1 in 500). When compared to control groups with the same risk profile, the added risk appears negligible.
Bottom line: Amnio adds ~0.3% miscarriage risk; CVS adds ~0.2%. Much safer than the old 1-in-200 figure.
Elective Induction at 39 Weeks
ARRIVE Trial (NEJM 2018) · 6,106 low-risk first-time mothers
The ARRIVE trial overturned the belief that induction increases cesarean risk. First-time mothers randomly assigned to induction at 39 weeks actually had LOWER C-section rates (19% vs 22%) compared to waiting for spontaneous labor. There was no difference in newborn outcomes. This led ACOG to say it's reasonable to offer elective induction at 39 weeks.
Bottom line: In the ARRIVE trial, elective induction at 39 weeks did not increase caesarean rates and slightly reduced them.
Food Safety in Pregnancy
CDC Safer Food Choices Guidelines · National surveillance data on pregnancy-related infections
Pregnant women are 10x more likely to get Listeriosis (CDC data). Listeria is found in unpasteurized cheese, deli meat, and smoked fish. Toxoplasmosis comes from undercooked meat and cat litter. FDA requires sushi-grade fish be frozen to kill parasites, making restaurant sushi generally safe. The CDC's top recommendations: avoid unpasteurized dairy, heat deli meats, wash produce thoroughly.
Bottom line: Focus on Listeria (raw cheese, deli meat) and Toxoplasmosis (undercooked meat). Sushi is generally safe.
Weight Gain During Pregnancy
Goldstein 2017 JAMA meta-analysis · Meta-analysis of 1.3 million pregnancies (23 studies)
This JAMA meta-analysis found that weight gain below IOM guidelines increases risk of preterm birth and small babies, while gain above guidelines increases cesarean risk and large babies. However, the absolute risk differences are modest. Pre-pregnancy BMI has a larger effect than pregnancy weight gain. The IOM guidelines (25-35 lbs for normal weight) are reasonable targets, not strict cutoffs.
Bottom line: Both too little and too much gain carry risks, but pre-pregnancy weight matters more.
Miscarriage Causes
ACOG Clinical Guidance · Expert consensus from the American College of Obstetricians and Gynecologists
About 10-20% of known pregnancies end in miscarriage, mostly in the first trimester. Approximately 50-70% of first-trimester miscarriages are caused by chromosomal abnormalities that occur randomly at conception, not anything the mother did or did not do. Exercise, sex, stress, and moderate caffeine don't cause miscarriage. Seeing a heartbeat at 8 weeks drops risk to about 3%.
Bottom line: Most miscarriages are chromosomal and unavoidable. It's not your fault.