Third Trimester Checklist: What the Research Says to Prioritize Before Baby

The Checklist Items the Research Ranks Highest Are Decisions, Not Errands

If you sort a third trimester checklist by measured effect on a baby's health, two items rise to the top, and neither one is a purchase. Both are vaccines, and both are worth describing here the way the research describes them, because the decision about whether to have either one is yours, made together with your doctor or midwife. What follows is what the studies and the medical organizations report, not a recommendation about your own care.

The first is the whooping-cough vaccine, Tdap. The Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists both describe it as recommended in every pregnancy, given between 27 and 36 weeks. A large case-control evaluation by Skoff and colleagues, published in Clinical Infectious Diseases in 2017, found that giving Tdap in the third trimester was about 78% effective at preventing whooping cough in infants younger than two months, and roughly 90% effective at preventing the hospitalizations that come with it. That window matters because the protection is built to transfer across the placenta and cover a newborn during the weeks before a baby can be vaccinated directly. This is the calmest corner of the vaccine conversation, with the two major US obstetric and public-health bodies aligned on it for years.

The second, the maternal RSV vaccine, is newer, and the guidance around it is both narrower and, as of 2026, more contested. The original evidence is strong: the MATISSE trial, published in the New England Journal of Medicine in 2023 by Kampmann and colleagues across 18 countries, found the single-dose vaccine about 82% effective against severe RSV illness in infants during their first 90 days. The current recommendation is specific. ACOG and the CDC describe a single dose between 32 and 36 weeks, in a first eligible pregnancy, given seasonally from roughly September through January, for those not delivering within two weeks. There is also an alternative path: a monoclonal antibody given to the baby after birth protects infants whose mothers were not vaccinated, so this is a vaccine-or-antibody choice rather than a protect-or-don't one.

Two caveats belong here, because a checklist that hides them is not worth trusting. First, the CDC has reaffirmed a possible link between the maternal RSV vaccine and a small increase in high-blood-pressure disorders of pregnancy, which is part of why the timing window is what it is. Second, in early 2026 ACOG began publishing its own maternal immunization schedule separately from the federal one, after the two diverged on several pregnancy vaccines. None of that tells you what to do. It is exactly why this belongs in a conversation with your own provider, who can lay out the benefits and the risks against your specific situation. The decision is entirely yours to make. For a sense of why these early weeks of protection carry so much weight, our look at how a baby's brain and body develop before birth covers just how much is still being built in the third trimester.

The Most Famous Checklist Habit Has Surprisingly Thin Evidence Behind It

Almost every pregnancy checklist tells you to count your baby's kicks, and the largest study ever run on the idea could not show that a formal counting program prevents stillbirth. This is the item people are most surprised to see questioned, so it is worth being precise about what the research did and did not find.

The study is called AFFIRM, published in The Lancet in 2018 by Norman and colleagues. It was enormous, covering more than 409,000 pregnancies across 33 hospitals in the UK and Ireland, and it tested a structured package that taught mothers to track fetal movement and report any decrease promptly. Compared with usual care, the package did not produce a statistically meaningful drop in stillbirth, and it was linked to more inductions and cesarean deliveries. A formal daily counting protocol, in other words, did not deliver the safety benefit that the practice is usually sold on.

Here is the part that still stands, and it matters: paying attention to your baby's movements is reasonable, and reporting any clear, sustained decrease to your provider promptly is sound advice that the trial does not undercut. What the evidence does not support is the idea that a strict counting ritual is a guarantee, or that hitting a magic number each day is what keeps a baby safe. The reassurance many checklists attach to kick-counting is larger than the science behind it. If your baby's pattern of movement changes noticeably, that is the clearest reason to pick up the phone, and the part of this worth holding onto. Babies are already doing a remarkable amount in there, as our piece on what your baby can do in the womb lays out, and their movement is part of that story.

Where You Fall Asleep Matters More Than Where You Wake Up

If there is a sleep item that belongs on a third trimester checklist, it is this: in late pregnancy, settling to sleep on your side rather than flat on your back is associated with lower risk, and the side you wake up on is not the thing to worry about. The distinction is the whole point, and most checklists either skip it or state it in a way that creates needless 3 a.m. panic.

The strongest evidence comes from an individual-participant analysis published in EClinicalMedicine in 2019 by Cronin and colleagues, which pooled data from five separate studies. Going to sleep on the back in late pregnancy was associated with about two-and-a-half times the odds of late stillbirth compared with going to sleep on the side. The leading explanation is mechanical: lying flat lets the growing uterus press on a major blood vessel, which can reduce flow to the baby. The same analysis found no meaningful difference between the left side and the right, which is good news for anyone who has spent the night anxiously trying to stay on one specific side. Either side is fine.

The practical translation is gentler than the statistic sounds. The finding is about the position you deliberately settle into when you fall asleep, not about policing yourself through the night. If you wake up on your back, the research is not telling you something went wrong; you simply roll back to your side and carry on. Arranging a pillow behind your back to make side-sleeping the path of least resistance is about the extent of the action item here. Everything else about third-trimester sleep, including the part where it becomes hard to get comfortable, is its own separate challenge.

A Few Things Happen on a Real Medical Timeline, and the Weeks Are Specific

The time-sensitive parts of a third trimester checklist follow a medical calendar, and a few of them have precise weeks that popular lists routinely get wrong. Organizing the real checklist by week is more useful than a generic to-do dump, because the actions that matter are gated to specific points in the pregnancy.

Entering the third trimester, the gestational diabetes screen sits at 24 to 28 weeks; ACOG describes this as a routine test for all pregnant patients, most often the glucose drink followed, if needed, by a longer tolerance test. From around 28 weeks onward, prenatal visits typically shift from monthly to every two weeks, and then to weekly as you approach the due date, which is a normal escalation rather than a sign anything is off. The vaccine windows discussed earlier fall across this same stretch, with Tdap from 27 weeks and the RSV conversation around 32 to 36 weeks.

Then there is the group B strep swab, which is the single item checklists most often misdate. Since 2019, ACOG has recommended screening at 36 0/7 to 37 6/7 weeks, a five-week-validity window, updated from the older 35-to-37-week timing that still circulates on many blogs. Group B strep is a common, usually harmless bacterium, and a positive swab simply means antibiotics during labor to protect the baby, so the value of the test is getting it at the right week. If a checklist tells you 35 weeks, it is quoting guidance that was replaced. Everything past this point starts to overlap with life at home, which our guide to the first week with a newborn picks up where this timeline ends.

The Checklist Staples the Evidence Quietly Does Not Support

Several beloved third trimester checklist items have less science behind them than their popularity suggests, and knowing which ones can save you money, time, and a surprising amount of guilt. None of this argues against doing things that bring you comfort or confidence. It is an argument against believing a product or a class will deliver an outcome the research does not promise.

Start with the stretch-mark aisle, one of pregnancy's most reliable expenses and least supported. A Cochrane review by Brennan and colleagues found that topical creams and oils applied during pregnancy did not prevent stretch marks, and a 2015 review in the British Journal of Dermatology by Korgavkar and Wang reached much the same verdict for the most popular options, cocoa butter and olive oil among them. Whether stretch marks appear has far more to do with genetics and how much the skin stretches than with what gets rubbed into it. Moisturizing because dry pregnant skin itches is a perfectly good reason on its own; preventing stretch marks just is not a promise the evidence backs.

Antenatal breastfeeding classes are the next gentle surprise. A Cochrane review by Lumbiganon and colleagues found that breastfeeding education on its own, before birth, showed no clear effect on how long women went on to breastfeed. The takeaway is to take a class if it builds your confidence and teaches you the mechanics, while knowing that the support that moves the needle tends to be the hands-on help available after the baby arrives, not the prenatal session. The same modest-evidence pattern shows up with rigid birth plans: a 2019 systematic review by Mirghafourvand and colleagues concluded there was not enough evidence to say that birth plans improve the birth experience or satisfaction. What tends to help is the collaborative version, a flexible set of preferences worked out with your provider rather than a fixed script, since labor has a way of ignoring scripts.

One real phenomenon deserves a fair hearing in the same breath. The urge to clean and organize in the final weeks, the thing everyone calls nesting, was documented as a real third-trimester behavioral pattern in a 2013 study by Anderson and Rutherford in Evolution and Human Behavior. The caveat is that it is not a reliable sign that labor is imminent, and the hormonal storytelling around it is not well established. Channel the energy productively if it shows up, but do not read it as a countdown clock.

The Preparation Almost No Checklist Mentions

The item missing from nearly every third trimester checklist is the one with the most evidence on the parenting side: a plan for your own mental health after birth, made before the birth. This is the preparation that gets filed under vague self-care, when the research treats it as one of the more consequential things you can set up in advance.

Part of why it helps to think about this early is gentle, not scary: these feelings often begin before anyone expects them to. In a large screening study published in JAMA Psychiatry in 2013, Wisner and colleagues found that among new mothers who screened positive for depression, the low mood had started after the birth for about 40%, but during pregnancy for another third, and even before pregnancy for roughly a quarter. So if the early weeks feel heavier than you pictured, it is not a sign you did anything wrong, and you are in very good company. That is the whole reason to set something up in advance, while you have the bandwidth, rather than trying to build a safety net with a newborn in your arms. In 2023 ACOG released its first guideline devoted to screening for depression and anxiety through pregnancy and after birth, which is a quiet acknowledgment from the field that this matters as much as any physical checkup. Your plan can be small and kind: a date on the calendar to check in with yourself with real honesty, the name of someone you could call, and one trusted person who agrees to keep an eye on you and ask real questions. None of it has to be perfect. It just has to exist before you need it, so that reaching for help feels like following a plan rather than admitting defeat.

There is a quieter, hopeful thread in this research too. The IMPACT BCN trial, published in JAMA Network Open in 2023 by Crovetto and colleagues, found that mothers assigned to a structured Mediterranean-diet program or a stress-reduction program during pregnancy had children who scored modestly higher on cognitive and social-emotional measures at age two. The effects were small, and the authors are careful to frame them that way, so this is a reason to eat well and tend to your stress, not a guarantee of anything. Still, it points at the same idea: what supports you in these weeks tends to support the baby too.

There is one piece of newborn preparation worth adding because it costs almost nothing and lines up neatly with how babies arrive: setting up what your baby will first be able to see. Newborn vision is blurry, focusing best at roughly 8 to 12 inches, about the distance from a feeding baby's eyes to your face, and newborns are drawn to bold, high-contrast patterns, according to the American Optometric Association. A few high-contrast images near the changing table or bassinet meet a newborn's visual system exactly where it starts, which is the logic behind tools like our high-contrast flashcards designed for those first weeks. If you want the longer view of how a baby's sight sharpens over the first months, our guide to what newborns can see, week by week follows the whole arc, and the broader rhythm of those first days lives in our newborn care basics.