• During your third trimester, the fetus will grow from about the size of an eggplant to a watermelon.
• Third-trimester symptoms include cramps, difficulty sleeping, and Braxton Hicks contractions.
• Preeclampsia is a concern during this time, so it's important to monitor your blood pressure.

The third trimester of pregnancy, which starts at week 27, is the home stretch. During this period, your body is preparing for labor and your baby is getting ready to come into the world.

As a result, the third trimester can be exciting as well as physically and emotionally challenging. It's not unusual to be anxious at the prospect of labor, says Sherry Ross, MD, an OB-GYN with her own private practice.

In the weeks leading up to delivery, the baby will finish developing hair and skin and shift into a head down position in preparation for birth. Here's a more detailed weekly breakdown of what you can expect in the last trimester of pregnancy.

27 to 28 weeks pregnant

• Size of baby: Around 10 inches from crown to rump and a little over two pounds, roughly the size of an eggplant.
• What's developing in the womb: The baby's brain and vital organs, like the lungs and liver, continue to mature.
• Common symptoms: Leg cramps at night, difficulty sleeping, and frequent urination are common third-trimester symptoms, says Ross. You may also find it difficult to take a deep breath as the growing baby presses against your rib cage.
• What to look out for: In the third trimester, your healthcare provider may want to see you more frequently: Every two weeks at first and then weekly as your due date nears. You should report any of the following symptoms: spotting or bleeding, uterine cramping, lower abdominal pain, persistent headaches, nausea and vomiting, and decreased fetal movement, says Ross.

29 to 30 weeks pregnant

• Size of baby: Around 10.5 inches and three pounds, roughly the size of a cauliflower.
• What's developing in the womb: The baby's lungs are more developed and the baby is now able to breathe and cry. The baby also starts developing other reflex actions, like the ability to suck and swallow.
• Common symptoms: Hormonal changes can cause symptoms like heartburn, constipation, back pain, hemorrhoids, or varicose veins, says Ross.
• What to look out for: The baby should be very active around this stage; the fluttering sensations you felt in the second trimester will probably be replaced by sharp jabs and kicks that may knock the wind out of you. The baby should move approximately ten times every two hours. Pay attention to your baby's movement patterns and inform your healthcare provider if your baby isn't moving this much.

31 to 32 weeks pregnant

• Size of baby: A little over 11 inches and four pounds.
• What's developing in the womb: The baby's hair, eyebrows, and eyelashes.
• Common symptoms: Your breasts may start to leak colostrum, a fluid that nourishes your baby for a few days before your milk comes in. It may be thick or yellowish, or thin and watery.
• What to look out for: By week 32, the baby is often lying down head first, in preparation for delivery. Your healthcare provider will probably check your baby's position at each visit. If your baby is not in position at this point, it's not a cause for concern just yet, since you still have some weeks to go.

33 to 34 weeks pregnant

• Size of baby: Almost 12 inches long and 4.5 pounds, about the size of a pineapple.
• What's developing in the womb: The baby's bones start to harden, although the bones in the skull remain soft to make it easier for the baby's head to come through the birth canal.
• Common symptoms: As you approach your due date, you may have stronger and more frequent Braxton Hicks contractions, says Ross. These contractions are typically irregular and may feel like a tightness in your tummy. Contact your healthcare provider if they become regular and increase steadily, as that could be an indication you're going into labor.
• What to look out for: Sudden weight gain, headaches, swelling in your face and hands, and vision problems can be a sign of preeclampsia. Preeclampsia can be life-threatening for you and/or the baby and requires immediate medical aid. Since the main red flag for preeclampsia is high blood pressure, your doctor will take regular readings during this time of pregnancy.

35 to 36 weeks pregnant

• Size of baby: Around 12.5 inches and 5.5 pounds, or the size of a honeydew melon.
• What's developing in the womb: The baby starts to gain weight rapidly and starts to look less wrinkly and more smooth and plump as a result. At this point, the baby's lungs and digestive system are fully developed, so if you deliver now, the baby would be able to breathe and suckle milk.
• Common symptoms: If this is your first pregnancy, the baby's head may drop down into your pelvis at this time. With the baby no longer pushing up against your stomach, you may be more comfortable, have less heartburn, and a better appetite.
• What to look out for: Around this time, your healthcare provider will probably want to see you once a week and will need to keep checking if your cervix has started thinning or dilating. Going into labor before 37 weeks is considered premature.

37 to 38 weeks pregnant

• Size of baby: Around 13.5 inches long and 6.5 pounds, roughly the size of a small pumpkin.
• What's developing in the womb: The baby's genitals develop fully around this time. In babies with penises, the testicles drop into the scrotum and in babies with vaginas, the labia is formed.
• Common symptoms: The rate at which the baby gains weight slows down, so your weight gain may follow suit. The baby's increased size means there isn't much room to move around, so you may feel fewer, but more forceful movements. You may have to urinate more frequently because the baby is pressing down on your bladder. You may also lose your mucus plug, which is a lump of mucus that seals your uterus off from infection. It can be clear, yellowish, greenish, or tinged with blood.
• What to look out for: Your pregnancy is now considered full-term, so you should be meeting your baby soon. Most people deliver between weeks 37 and 42, says Ross. Additionally, it's rare nowadays for a doctor to let a pregnancy go past 41 weeks. Since the baby could come anytime, keep your hospital bag ready, so you can grab it in a hurry.

39 - 40 weeks pregnant

• Size of baby: Roughly 14 to 20 inches long and weighs 6-9 pounds, around the size of a watermelon.
• What's developing in the womb: The hair and waxy coating that protect the baby in the womb usually disappear by this time.
• Common symptoms: You may experience Braxton Hicks contractions that are as strong as labor contractions; however, unless they become regular and start coming closer together, they may still be false labor. Your water may also break around this time, which could be one large gush or a slower stream.
• What to look out for: You may find yourself waiting a week or two for your baby to arrive if this is your first pregnancy, or if you've had an overdue pregnancy in the past. Your doctor may induce labor at 39 weeks.

Insider's takeaway

By the third trimester you'll probably be both excited to meet your baby and nervous about delivery. As your body prepares for labor, you'll need to check in with your healthcare provider regularly.

The most important things to keep track of during the third trimester include paying attention to daily fetal movement, getting adequate rest, eating a healthy and well-balanced diet, and preparing for labor and the arrival of your newborn, says Ross.