Nine Weeks and Counting
Week 31 is one of those weeks that doesn't come with a big milestone appointment or a dramatic shift. What it does come with is increasing awareness: of your belly, of your breath, of every time you need to get up to use the bathroom, and of the fact that in about nine weeks, everything changes.
The baby is practicing. You are preparing. The body is doing the quiet, essential work that doesn't make for dramatic stories but matters enormously for the finish line.
Your Baby This Week
Your baby is about the size of a coconut, measuring approximately 16.2 inches (41.1 cm) from head to heel and weighing around 3.3 pounds (1.5 kg) [1][2]. The body continues to fill out as fat deposits accumulate, and the skin is becoming less transparent as those layers deepen.
All five senses are functional. Your baby can see light filtering through the uterine wall, hear sounds from inside and outside your body, taste the amniotic fluid, detect smells dissolved in the fluid, and feel pressure and movement. The brain is processing and responding to all of this input continuously [2].
The irises can now dilate and contract in response to light. Fingernails and toenails are nearly fully grown. If born now, a 31-week baby would need intensive care but has a very high survival rate with modern neonatal support [3].
Lung Surfactant: The Key to Breathing Air
The lungs are doing two things simultaneously this week: producing surfactant and practicing breathing movements.
Surfactant is a slippery, detergent-like substance that coats the tiny air sacs in the lungs (alveoli) and keeps them from collapsing when your baby exhales. Without adequate surfactant, the lungs collapse after each breath, which is what causes respiratory distress syndrome in premature newborns [3].
The good news: surfactant production begins around 24 to 28 weeks and increases steadily through the third trimester. By 35 to 36 weeks, most babies have produced enough surfactant to breathe independently. By 31 weeks, the amount is increasing but not yet fully sufficient for life outside the womb without some support.
Your baby is practicing the mechanics of breathing by pulling amniotic fluid in and out of the lungs in rhythmic movements. These aren't real breaths, but they strengthen the diaphragm and respiratory muscles in preparation for the real thing [1]. You may occasionally feel a rhythmic, repetitive thumping sensation, very different from a kick: that's your baby having hiccups, which are a normal result of this breathing practice.
Braxton Hicks: What They Are and What They're Not
Braxton Hicks contractions are tightening sensations across the abdomen that can feel surprising or even uncomfortable, especially in the third trimester. They're sometimes called "practice contractions," and that's a reasonable description: the uterus is a muscle, and Braxton Hicks are low-intensity workouts [4].
What makes them different from real labor contractions:
- No pattern: Braxton Hicks are irregular. They don't come at predictable intervals and don't get closer together over time.
- They stop: Walking, drinking water, changing positions, and resting all tend to make Braxton Hicks ease off. Real labor contractions continue and intensify regardless of what you do.
- They don't build: Real contractions get longer, stronger, and closer together. Braxton Hicks stay about the same or fade.
- Timing: Braxton Hicks are more common in the afternoon and evening, after physical activity, or after sex or dehydration.
If you have more than four to six contractions per hour, they follow a pattern, or you feel any other signs of labor (pelvic pressure, lower back pain that comes and goes, vaginal discharge changes), call your provider [4].
Your Body at Thirty-One Weeks
- Frequent urination: The baby's head pressing on your bladder means you may feel the urge even immediately after going. This is a physics problem, not a bladder problem, and it gets worse before it gets better.
- Shortness of breath: The uterus is high enough now that it's significantly limiting your lung capacity. Moving more slowly helps. This typically improves when the baby drops into the pelvis in the coming weeks.
- Pelvic floor pressure: Increased weight and relaxin (the hormone that loosens ligaments) can make the pelvic floor feel heavy or achy. Pelvic floor exercises (Kegels) help maintain strength.
- Trouble sleeping: Positioning is the main challenge. A full-length pregnancy pillow that supports your belly, back, and knees simultaneously can make a meaningful difference.
- Nesting instinct: Many women notice a strong urge to organize, clean, and prepare the home in the third trimester. This is normal and, within reason, completely healthy. Just don't climb ladders.
The Emotional Side
"I am genuinely terrified of giving birth." About 16% of pregnant women experience severe fear of childbirth, a condition clinicians call tokophobia. It goes well beyond normal nervousness. If the thought of labor triggers panic, avoidance, or nightmares, you are not being dramatic. Your fear deserves clinical attention, not dismissal. Talk to your MomDoc provider about what specifically frightens you. Fear of pain, fear of loss of control, and fear of injury each have different management approaches, and knowing yours helps your care team prepare with you.
What MomDoc Wants You to Know
Week 31 is a good time to start putting your birth plan on paper. You don't need a lengthy document: a one-page outline covering your preferences for pain management, labor support, delivery preferences, and postpartum priorities is more useful than a detailed manifesto. Your provider can help you understand which preferences are feasible given your specific situation.
The most important thing to know about birth plans: they are starting points for conversations, not contracts. Labor rarely follows a script. The goal is to feel informed and heard, not to guarantee a specific outcome.