Week 38
Your baby is the size of a leek
Two weeks to your due date. The calendar feels like it's standing still and your body is loudly complaining. Per Palmeira et al. (J Immunol Res, 2012), most of your baby's maternal antibody supply crosses the placenta during the third trimester. You're deep in that window now. Here's what week 38 actually is.
Key takeaways
- Most maternal antibodies cross the placenta during the third trimester per Palmeira et al. (J Immunol Res, 2012). IgG is the only antibody class that transfers in significant amounts, and you're now in that window.
- Elective induction at 39 weeks may reasonably be offered to low-risk first-time mothers per ACOG/SMFM Practice Advisory (2018). In the ARRIVE trial of 6,106 women, the cesarean rate was 18.6% with induction vs 22.2% with expectant management (Grobman et al., NEJM 2018).
- A Bishop score of 6 or less is unfavorable for induction per ACOG's Cervical Ripening Clinical Practice Guideline (Obstet Gynecol, July 2025). The score determines whether your provider starts with cervical ripening before pitocin.
- Membrane sweeping increased spontaneous labor (RR 1.21) and reduced formal induction (RR 0.73) per Finucane et al. (Cochrane, 2020). Modest. Real. Worth asking about.
Your antibodies are crossing the placenta right now, and most of the transfer happens in the third trimester
Per Palmeira et al. (J Immunol Res, 2012), IgG is the only antibody class that crosses the placenta in significant amounts, and most of that transfer happens during the third trimester.
The mechanism is specific. A receptor called FcRn, expressed on the syncytiotrophoblast cells of the placenta, grabs your IgG and ferries it to your baby. IgG1 transfers most efficiently. IgG2 transfers least.
By delivery, your baby's IgG levels may actually be higher than yours. That borrowed immunity is what protects them through the first weeks of life while their own immune system finds its footing.
Your baby is now roughly 19 to 20 inches long and 6 1/2 to 7 1/2 pounds, per Mayo Clinic.
The lanugo (that downy hair) is almost entirely gone. The vernix is thinner now, lingering mostly in skin folds. Head and abdominal circumferences are roughly the same size, which means newborn proportions have arrived.
If your baby is head-down, the head may have started to settle deeper into your pelvis. That's called lightening. You might breathe more easily and eat more comfortably. The bathroom is a different story.
Why your provider may run a Bishop score this week, and what 'cervical ripening' actually means
Per ACOG/SMFM Practice Advisory (2018), elective induction at 39 weeks may reasonably be offered to low-risk nulliparous women. That guidance came out of the ARRIVE trial.
Per Grobman et al. (NEJM, 2018), in 6,106 low-risk first-time mothers, the cesarean rate was 18.6% with induction at 39 weeks versus 22.2% with expectant management (RR 0.84, 95% CI 0.76 to 0.93). The primary outcome of perinatal death or severe neonatal complications was not significantly different between groups.
So the conversation now turns to your cervix.
Per ACOG's Cervical Ripening Clinical Practice Guideline (Obstet Gynecol, July 2025), the Bishop score adds five things: dilation, effacement, station, consistency, and position. A score of 6 or less is unfavorable. 8 or more is favorable.
If the score is low and induction is planned, your provider may discuss cervical ripening before pitocin. A balloon catheter. A prostaglandin. Sometimes both.
Membrane sweeping is the other option. Per Finucane et al. (Cochrane, 2020), sweeping increased spontaneous labor (RR 1.21, 95% CI 1.08 to 1.34) and reduced formal induction (RR 0.73, 95% CI 0.56 to 0.94).
Contact your provider right away if you have heavy bleeding, fluid leakage, severe headache or vision changes, upper-belly pain, or a sustained drop in your baby's movement.
For dads
Here's your move:
Build a 'last call' checklist this weekend. Not the hospital bag. That's been in the car since week 36. The 'last call' is the list of people who get the text when labor starts. Parents. Siblings. The dog sitter. Your boss. Your boss's boss in case the first one is on vacation. Type the actual text now ('We're heading in, more soon'). Save the L&D direct line one tap away. Print her insurance card and put a copy in the bag in case her phone dies. The version of you with a list outperforms the version of you trying to remember names at 3 AM.
Real talk:
She's exhausted in a way that's hard to describe. Not 'rough week at work' exhausted. 'I haven't slept more than three hours straight in seven weeks and there's a person inside me using my ribs as monkey bars' exhausted. Skip the pep talks. Don't tell her she's almost there. The word 'almost' covers anything from tonight to two more weeks, and that's a brutal range when every hour feels like a day. What lands: ask 'What's the one thing that would help today?' Then go do that. Don't narrate. Don't make it a project. Quiet wins. You'll need this muscle in the newborn shift.
Common concerns
What's a Bishop score and do I need to know mine?+
It's a 0-13 cervical readiness score per ACOG's Cervical Ripening Clinical Practice Guideline (Obstet Gynecol, July 2025), built from dilation, effacement, station, consistency, and position. You don't need to memorize the number. If induction is on the table, ask what your score is and what your provider plans if it's under 6.
Should I do a membrane sweep if my provider offers one?+
Per Finucane et al. (Cochrane, 2020), sweeping modestly increases spontaneous labor and reduces formal induction. It's brief and mildly uncomfortable, and the Cochrane review found no significant safety concerns in low-risk pregnancies. Ask about timing and whether your cervix is open enough for a sweep to even be possible.
Can I refuse a 39-week induction if my provider offers one?+
Yes. Per ACOG and SMFM, the recommendation is to offer elective 39-week induction to low-risk first-time mothers, not require it. Shared decision making is the standard. If you'd rather wait for spontaneous labor and your pregnancy is healthy, that's a reasonable choice. Talk it through with your provider.
My baby just dropped. Does that mean labor is starting?+
Not necessarily soon. Lightening can happen days or weeks before labor, especially in first pregnancies. It's a sign of progress, not a countdown. Regular timed contractions, your water breaking, or a sustained low backache with increasing pressure are the actual go-to-the-hospital signals.
Product picks for week 38
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Frida Mom 11pc Postpartum Essentials Kit
Hospital-bag postpartum bundle: disposable underwear, ice maxi pads, healing foam, peri bottle, pad liners. Ready for any-day delivery.
BABYGO Birthing Ball with Exercise Book Set
65cm anti-burst ball with trimester-specific guide. The standard tool for gentle pelvic activity that may help the baby descend now that lightening has started.
Konssy 3-Pack Muslin Swaddle Blankets, 47 x 47 inches
Newborn-sized muslin swaddles for the going-home bag and first weeks at home. Breathable for the temperature regulation a term newborn still needs help with.
Sources
- Palmeira P et al. IgG Placental Transfer in Healthy and Pathological Pregnancies. J Immunol Res. 2012;2012:985646 — https://onlinelibrary.wiley.com/doi/10.1155/2012/985646
- Grobman WA et al. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women. N Engl J Med. 2018;379(6):513-523 — https://pubmed.ncbi.nlm.nih.gov/30089070/
- ACOG/SMFM, Clinical Guidance for Integration of the Findings of the ARRIVE Trial (Practice Advisory, August 2018) — https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2018/08/clinical-guidance-for-integration-of-the-findings-of-the-arrive-trial
- ACOG, Cervical Ripening in Pregnancy: ACOG Clinical Practice Guideline No. 9 (Obstet Gynecol, July 2025) — https://journals.lww.com/greenjournal/fulltext/2025/07000/cervical_ripening_in_pregnancy__acog_clinical.30.aspx
- Finucane EM et al. Membrane sweeping for induction of labour. Cochrane Database Syst Rev. 2020;2:CD000451 — https://pubmed.ncbi.nlm.nih.gov/32103497/
- Mayo Clinic, Fetal Development: The 3rd Trimester (March 2025) — https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20045997
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn how we create our content.