The Last of the Second
Week 27 is the final week of the second trimester. Next week, at 28 weeks, you cross into the third trimester, the last chapter before birth. For many women, that transition feels both exciting and quietly daunting. The second trimester is generally considered the "easier" phase of pregnancy: more energy, less nausea, a belly that is visible but not yet overwhelming. The third trimester is something else.
You've done a lot of hard work getting here. Week 27 is worth recognizing.
Your Baby This Week
Your fetus is now roughly the size of a cauliflower, measuring about 14.4 inches (36.6 cm) from head to heel and weighing approximately 2 pounds (875 grams) [1]. The brain and nervous system are the focus of the most dramatic development.
- REM sleep is active. Your baby is entering periods of REM (rapid eye movement) sleep, the phase associated with dreaming in adults. Researchers believe REM sleep in the fetus plays an important role in nervous system development and sensory processing [2].
- Sleep-wake cycles are established. You may have noticed that your baby is active at predictable times, often late at night, and quieter at others. These cycles are now fairly consistent and reflect a maturing circadian rhythm [2].
- The brain surface is folding. The characteristic folds and grooves of the cerebral cortex, the gyri and sulci, are developing more rapidly now. This folding dramatically increases the surface area of the brain, allowing for more neural connections [2].
- Eyelids open and close regularly. Your baby blinks, moves their eyes, and responds to light with increased movement if a bright light is held close to your abdomen [4].
- Lung maturity is progressing. Surfactant production continues to increase. A baby born at 27 weeks would almost certainly need respiratory support, but survival rates with NICU care are now above 90 percent at this gestational age [3].
The Third Trimester: What Changes
The transition from the second to the third trimester is not a cliff. You will not feel dramatically different on the day you hit 28 weeks. But there are real changes in how pregnancy is managed and how your body will feel over the coming weeks.
In terms of prenatal care:
- Visits become more frequent. Starting around week 28 to 32, most providers schedule appointments every two weeks rather than monthly. After week 36, visits typically become weekly [4].
- Important vaccinations are due at week 28. ACOG recommends the Tdap vaccine (for pertussis, diphtheria, and tetanus) in every pregnancy, ideally between weeks 27 and 36. This allows the antibodies you produce to cross the placenta and provide some protection to your newborn before they are old enough to be vaccinated themselves [5]. Flu vaccine is also recommended if you haven't already had it.
- RhIg injection at week 28. If you are Rh-negative, you will receive a RhoGAM injection at this visit to prevent sensitization.
- Growth monitoring increases. Fundal height is checked at every visit. If there are concerns about growth, additional ultrasounds may be ordered.
In terms of how you'll feel:
Sleep becomes harder. The belly makes comfortable positions scarce. The diaphragm has less room, so shortness of breath is common. The bladder is under constant pressure. Heartburn intensifies for many women. The third trimester is physically demanding, and you are not wrong to feel apprehensive.
The payoff is the end of it: a baby.
Your Body at Twenty-Seven Weeks
- Shortness of breath. The uterus is rising toward the diaphragm, reducing the space available for your lungs to fully expand. Mild breathlessness with exertion is normal. Sudden or severe shortness of breath, especially with chest pain, requires immediate evaluation.
- Restless legs. A crawling or uncomfortable sensation in the legs that worsens at rest, particularly at night, is a recognized pregnancy symptom. The cause is not fully understood but may be related to iron deficiency or dopamine changes. Mention it to your provider, especially if it is significantly disrupting sleep, as it can sometimes indicate treatable deficiencies.
- Increasing pelvic pressure. The baby's weight is bearing downward. You may feel pressure in the pelvis or a heaviness in the vaginal area. This is normal but increases throughout the third trimester.
- Forgetfulness. "Pregnancy brain" is a commonly reported symptom. Research suggests that memory and attention can be mildly affected during pregnancy, partly due to sleep disruption, hormonal changes, and the reorientation of cognitive resources toward the pregnancy. Write things down. Give yourself grace.
The Emotional Side
"Thirteen more weeks feels impossible. I don't know if I can do this." Third-trimester exhaustion is cumulative. By week 27, you have been managing physical discomfort, emotional upheaval, and logistical planning for over six months. Feeling like you cannot sustain this pace is not weakness. It is an accurate assessment of a demanding situation. The energy for the final stretch does come, but it often arrives in waves rather than as a steady supply. Tell your provider if the exhaustion is accompanied by persistent sadness or hopelessness, as those can signal something beyond normal fatigue.
What MomDoc Wants You to Know
Your week 28 appointment is one of the most important prenatal visits of the entire pregnancy. Glucose screening results (if not already completed), RhIg injection, Tdap vaccine, repeat blood work including CBC and antibody screening, and a fundal height check will all likely happen at that visit. Make sure you have it scheduled.
You are one week from the third trimester. The sleep-wake cycles your baby has already established in the womb will be the same rhythms you'll be responding to when you wake at 2 a.m. to feed them. They have been practicing for this. So have you.