Week 18 Pregnancy: Weight Gain, Baby Position & Back Pain

Week 18 Pregnancy Weight Gain Baby Position and Back Pain (1)

Your pregnancy is rolling along! You’ve made it to week 18 of your pregnancy! Let’s talk about your weight gain, baby’s position, symptoms like back pain and… big feet? And as always, let’s check in on that cute little one!

Estimated reading time: 8 minutes

Week 18 Pregnancy: How Big is Baby?

At week 18 — 16 weeks from conception — your little one is now about the size of a bell pepper. Crown to rump, baby is around 5 to 5 1/2 inches long, and weighs a little over five ounces (1). What else is going on with baby’s development?

  • Your tiny one is actually starting to look human now! His ears are beginning to stick out from his head and his eyes have finally moved to totally forward-facing (2). It’s incredible to look back at week 8 compared to week 18!
  • He has regular patterns of sleep and wakefulness. He can also be awakened from sleep by noises and your movements (3).
  • If your baby is a girl, her ovaries have formed and even contain eggs!
  • If your baby is a boy, his testes have begun to descend.

Week 18 Pregnancy: Pregnant Belly

You are probably sporting quite the cute little bump these days! Your uterus is around the size of a cantaloupe, and the fundus (remember, that’s the top of the uterus) is only about an inch below your bellybutton.

Weight Gain

Though weight gain varies, you’ve likely gained around 10 to 13 pounds so far. Here’s where some of that weight gain is going (1):

  • 6 ounces for baby
  • 6 ounces for the placenta
  • 11 ounces of amniotic fluid
  • 11ounces for your uterus
  • 6 1/2 ounces each in increased weight in your breasts

The rest of the weight gain is due to an increase in blood volume and other maternal stores. Maternal stores refers to the extra fat gained during pregnancy; it’s purpose is largely to prepare the body for breastfeeding.

If you’ve gained significantly more than this amount so far and you’re concerned, talk to your doctor or midwife. You want to be sure your weight gain is steady and consistent, enough to nourish your baby and your body, but not so much as to bring on extra risks or unpleasant side effects. If your weight gain is higher than your provider prefers at this point, he or she may refer you to a nutritionist.

Week 18 Pregnancy: Baby Position

Baby still has a lot of space to move around, and a lot of time before he or she will settle into a final position. But let’s talk about positions and presentations, so you’ll have an idea of what these terms mean as your caregiver starts to talk about them in the coming weeks and months.

Baby’s Presentation

When we refer to baby’s presentation in the uterus, that describes which part of your baby is lying over the cervix, or what part is facing down.

Vertex Presentation

This is the desired head-down position. It’s the easiest and safest presentation to have a vaginal birth. Fortunately, by the last month of pregnancy, 95% of babies will be vertex (4).

Breech Presentation

Most babies who are not vertex at birth are breech, meaning that the head is up and the bottom is down. There are different breech presentations that describe where baby’s legs are.

  • In a frank breech presentation, the bottom is down but the legs are up, with the feet near the baby’s head.
  • In a complete breech presentation, the knees are bent, legs usually crossed in front of the body, so that the feet are near the bottom.
  • A footling breech has one or both feet below the bottom, so that if they were delivered that way, a foot would be the first body part to emerge.

A vast majority of providers won’t attempt to deliver a breech baby vaginally, so in order to avoid cesarean delivery, your doctor may talk to you about the possibility of attempting to turn baby via external cephalic version.

Rare Presentations

Less common presentations include transverse lie, where the baby is sideways in the uterus instead of head up or down. (Note that while these presentations are uncommon at birth, a transverse position is the norm for baby earlier on in pregnancy.) Other rare positions at birth include shoulder, face, or brow presentations.

Baby’s Position

Another term your provider might use is position. This is not the same as presentation. Remember that presentation refers to which part of the baby is over the cervix. Position, on the other hand, refers to whether the baby is facing mom’s front, back, or side. The back of the baby’s head is called the occiput, and position is described by the direction the occiput is facing.

  • Occiput anterior (OA) – The back of your baby’s head is pointing toward your anterior, or front. (Baby’s face would be looking toward your spine.) This is the best position (aka. provides the easiest movements for baby to descend through the birth canal) and by the time baby is delivered, most are OA.
  • Occiput posterior (OP) – The back of baby’s head is facing your posterior, or back. (Baby’s face would be looking out your tummy.)
  • Occiput transverse (OT) – The back of baby’s head is facing your side rather than front or back.

Week 18 Pregnancy: Symptoms

Back Pain

One of the most common discomforts experienced by pregnant women is back pain. You haven’t gained much weight at this point, and you don’t usually hear about back pain in a non-pregnant person who happens to gain a little weight. So why is back pain such a universal symptom in pregnancy?

What Causes Back Pain in Pregnancy?

A combination of factors contribute to back pain. Hormones relax the joints in your body during pregnancy; this is so that your pelvis can expand to deliver your baby. But unfortunately, it also means that all of your joints are a little “loose” during pregnancy (1). Additionally, your growing bump stretches out and weakens your abdominal muscles, meaning your back has to overcompensate for your weakened abs (3). Your bump also shifts your center of gravity, which changes your posture.

Think for a moment about the pictures you’ve seen of strong, beautiful women carrying pitchers of water on their heads. The reason they do it that way is because carrying on the head keeps the spine and muscles aligned properly, and is much easier than carrying a load out front. It isn’t the extra weight that’s so hard on a back, it’s the pulling in the wrong direction. Your sweet little pregnant belly is currently providing that wrong-direction pull.

What Can I do About Back Pain in Pregnancy?

  • Maintain good posture. Gravity is always exerting force on your joints, ligaments, and muscles. Good posture more evenly distributes that force, so some parts aren’t stressed excessively (4). “Good posture” means that your ears, shoulders, hips, and ankles are in a straight line. If it helps, imagine that you’re wearing a crown, and you need to keep it balanced by standing straight.
  • Stay active and continue exercising during pregnancy unless your provider has advised against it. Just stick to things like swimming, walking, and other low-impact activities. Check out some yoga poses that you may find helpful for back pain during pregnancy. And make sure you’re keeping your core muscles strong.
  • Don’t bend at the waist. If you need to lift something, squat instead of bending.
  • Wear shoes with low heels and good support. Heels tilt your body forward and this strains your lower back muscles.
  • Use an abdominal support garment. Most look like a girdle. They support the weight of your belly and take the strain off your back muscles.
  • Try a cold compress, a heating pad on the lowest temperature setting, or a rice sock.

Are My Feet Growing???

It may seem like there’s a never-ending list of symptoms that you didn’t even realize came with pregnancy. Today’s weird symptom…your feet seem to be growing. You may be noticing that your shoes don’t fit like they used to, even though you may not think your feet look swollen yet.

What causes your feet to grow during pregnancy?

There may be some water retention or swelling, and your overall weight gain may be a factor. However, a big culprit you may not have known about is relaxin. It’s the same hormone we just talked about with back pain — the one that causes your joints to relax. It also loosens the ligaments in your feet, causing the foot bones to spread (3). This often leads to permanent changes in shoe size even after baby is born.

Is there anything you can do to stop foot changes? You can try elevating your feet to help with swelling. But, if your problem seems to be more a result of bones spreading, you may just need to shop for new shoes.

Visit us again next week to see what’s going on in your body in week 19!

Kopa Birth’s online birthing classes allow you to prepare for a natural hospital birth from the comfort of your own home, 24/7. Enroll today in our free online childbirth class and start preparing for your natural birth!


  1. Glade, B.C., Schuler, J. (2011). Your Pregnancy Week by Week, 7th edition. First Da Capo Press
  2. “Fetal Development: What Happens during the 2nd Trimester?” Mayo Clinic, Mayo Foundation for Medical Education and Research, 8 July 2017, www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151.
  3. The American College of Obstetricians and Gynecologists. (2010). Your Pregnancy and Childbirth Month to Month, 5th edition
  4. Simkin, P. (2010). Pregnancy, Childbirth and the Newborn, 4th edition. Meadowbrook Press

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Meet Katie Griffin

I’m a registered nurse, Lamaze certified childbirth educator, and the mother of 7. I help women realize their dream of a natural, intimate, and empowering hospital birth.

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Your pregnancy is rolling along! You’ve made it to week 18 of your pregnancy! Let’s talk about your weight gain, baby’s position, symptoms like back pain and… big feet? And