Fetal Development Series: Part 4

September 25, 2025

Welcome back to the Fetal Development Series! This week we’ll be digging into Month 4, or the very beginning of Trimester 2. This month is filled with significant milestones. As a recap, here’s some of the Month 3 developments we’ve discussed in your fetus’s body and in your own body:

• The name of your baby has changed from embryo to fetus
• The bump likely isn’t quite there yet, but is coming soon
• Continued symptoms from Month 3
• Your baby’s major organ systems are continuing to grow quickly

A Little Bit About the Bump Again

As discussed in the last post in this series, when you show is quite subjective. It’s based on whether this is your first pregnancy, how many fetuses you’re pregnant with, your weight, height, and body shape, among other factors. But by the end of Month 4 is likely when most pregnancies will actually start to show themselves. 

To make the process fun and engaging, get a soft measuring tape, like this one, and measure your belly once a week, making note of your increase in a journal. Taking weekly or monthly selfies or having professional photography done (if financially feasible for you) is also a great way of seeing your progress. 

It’s also at this time where, if you don’t already have anything in your wardrobe, you should likely start searching for some maternity-friendly clothing. You’ve perhaps already realized that your favorite pair of jeans no longer fits quite right! 

Symptom-wise, you may have pain or soreness in your sides as your uterus expands (Pregnancy: Second Trimester). The skin on your belly may feel itchy as it stretches, so now’s a great time to bring out some shea butter. Stretch marks may appear around your hips, belly, bottom, thighs, and breasts.

Gender Reveal & Heartbeat

Hopefully you’ve been getting regular prenatal checkups from a healthcare provider. If not, it’s better late than never to make an appointment! Unless you’re determined to be higher risk by a provider, these appointments usually happen once per month. It’s also at this time that some healthcare providers can detect the gender of your fetus on an ultrasound scan. This may happen mid-way through Month 4 at the soonest, but likely happens closer to Month 5. If you’d prefer to keep the gender a secret, then of course you can request that your healthcare provider keep that result hidden from you. But otherwise, this is the time that you can think about having a gender reveal party, if you so choose. Other than determining the gender, your healthcare provider will monitor the fetal heartbeat.

Your Symptoms

The beginning of Trimester 2 is a fascinating time. Not only will you likely have access to the gender of the fetus and will be able to see your belly grow, the onslaught of symptoms that you may have been experiencing the past three months likely should be calming down. As you exit Week 12 and journey on through Week 16, symptoms like nausea, fatigue, mood swings, and tiredness should lighten up since your hormones aren’t quite as high. You may feel less irritable and have more energy. One reason for this calming down is because at this time your  “placenta is now feeding your baby, having taken over from the yolk sac, and once this happens your hormones will calm down a bit” (Week 12). Since this time is usually the calmest (between the more difficult first few months and labor), many women might find this stage of pregnancy the most enjoyable or the least challenging. 

Breast tenderness will also likely ease up, but your breasts may continue to gradually increase in size. The frequent need to pee may also lessen as your uterus grows up over the pelvic area, causing less direct pressure on your bladder (The Second Trimester). Backaches may occur because of your growing belly and breasts. Unfortunately, the symptoms of constipation, heartburn, and indigestion may continue, again due to hormones (The Second Trimester). 

Hormonally you may be not as challenged with tiredness and irritability, but still, the increase in estrogen and progesterone present may even cause bleeding in two forms: nosebleeds and red gums (The Second Trimester). If your gums happen to feel sore and even bleed, or if you have a nosebleed, take care not to worry too much, as this is a symptom some women experience, since your hormones are causing changes in your mucus membranes in those two areas (The Second Trimester). As you can imagine, this means practicing good oral hygiene is more important now than it’s ever been (not that it wasn’t important before). 

You may also experience varicose veins, headaches, and hemorroids. Not fun, of course, but part of the process. Another set of issues you may experience are UTIs or vaginal infections (like yeast infections/thrush or bacterial vaginosis/BV) (Pregnancy: Second Trimester). Keep a close eye on any vaginal changes, such as burning when you pee, discharge, or odd smells. If you have sore or swelling feet, ankles, and lower legs, this is normal at this time, as it’s caused by fluid retention, or edema (Bunce and Heine 2023).

Movement

I know one topic on any woman’s mind during pregancy is movement, or if you’d prefer to use the old-fashioned term, quickening. As you’ve likely already noticed if you’ve read my previous posts about this topic, every woman’s experience is unique, which means some women may feel movement sooner or later than others. But it’s at this stage, especially later on when Month 4 is closing and Month 5 is beginning, that you may start to feel slight fetal movement. With the fetus becoming more active as each day passes, it often doesn’t stay still. Many women describe movement as a gentle butterfly feeling. If you don’t feel movement yet, don’t worry. You may only start to feel it later on in Month 5 or the beginning of Month 6. Right now movement is sporadic and weak. Once the fetus becomes a baby that movement will grow more defined and frequent.

Eating & Weight Gain 

You may feel confused as to how much you should eat. Eating for two is something of a myth. Even though later on in Trimester 2 you should increase calories somewhat, eating enough calories for a whole other adult person would be far too much. Most resources suggest increasing to 200-300 extra calories per day. You can get this by eating something healthy but calorically dense, like bananas, avocados, nuts and seeds, whole grains, or small, infrequent amounts of low-mercury fish like salmon. This is more applicable to women further into Trimester 2, so right now, it’s a good idea to continue on with a good pregnancy diet for one. You’ll likely start or continue with any odd cravings (like food combinations you’ve never had before). 

As for weight gain, this will vary like most other pregnancy symptoms. Some women may gain quite a few pounds while others won’t gain much weight at all. This could depend on how high or low your BMI was prior to pregnancy and how many babies you’re pregnant with. But seeing the number on the scale increase, to some extent, is normal, since increased blood volume, your placenta, the baby itself, amniotic fluid, and larger breasts, among other things, are adding to that number (Mayo Clinic Staff 2024). Of course, if you happen to be under or overweight, the topic of weight gain and calorie consumption is something best discussed with a healthcare provider. 

Exercise

You’re likely also wondering if exercise is all right for you. While the first couple months of pregnancy were likely tiresome and more rest and sleep-focused, Trimester 2 (when your mood and energy will likely lighten up) is a good time to start doing exercises with a low possibility of injury, like yoga, walking, or swimming. The general rule of thumb is to not exercise for too long, too often, or, on the flipside, too infrequently.

Fetal Development

When you’re getting into Month 4, the major organ systems are pretty much set in place and are in the process of growing larger as the fetus gains length and weight. The risk of miscarriage is also much lower, as the majority of miscarriages happen within Trimester 1. Your fetus’s size will increase by more than seven times over the next few months (The Second Trimester). Also, your umbilical cord is thickening as it carries nutrients to your fetus (The Second Trimester). 

As we discussed in the Movement section, it’s at this point that the fetus may start to move, like turning from side to side, kicking, or even making a punch-like motion now that all its fingers and toes are separated, although this level of movement is more likely to happen later in Trimester 2. The fetus can also hear, and will be able to hear your heartbeat and any other bodily noises (like from your digestive organs), so feel free to talk to them or even sing! 

Some reading this may be familiar with a white substance called lanugo that babies are covered in when they’re born. It’s around this time that lanugo is forming to protect the fetus’s very sensitive, thin skin (Week 15). The fetus also is starting to look more like a human and less like a tiny alien. It’s facial features are aligning and it’s starting to grow all the smaller additions, like eyelashes, eyebrows, nails, and hair (Pregnancy: Second Trimester). Another development that seems superficial is the presence of thumb-sucking. Now that the fetus’s fingers are separated, it can suck on its thumb in preparation for being breastfed (Pregnancy: Second Trimester). Fingerprints and toeprints are forming and the fetus even goes through cycles of sleep and wakefulness (The Second Trimester). 

Conclusion & Recap

Remember, not all pregnancies are the same. Women can have a wide variety of symptoms and experiences, while others may be lacking in common symptoms. What’s important in Trimester 2 is to go to regular checkups and try to enjoy this middle-stage of pregnancy as much as you can (even if the symptoms are bothering you). 

For a recap, here’s some symptoms you may continue experiencing from previous weeks or may develop:

• Constipation
• Headaches
• Acid reflux/heartburn
• Swelling in legs, ankles, and/or feet
• Vaginal infections
• UTIs
• Itchiness on abdominal skin
• Soreness in sides
• Stretch marks
• Backaches
• Hemorroids
• Sore and/or bleeding gums
• Congestion and nosebleeds
• Varicose veins

And here’s a recap of a few points of fetal development:

• Growing in length and weight
• Hearing becomes possible
• Movement
• Thumb sucking
• Production of lanugo
• Cycling through sleeping and waking

Make sure to stay tuned for Month 5!

References

Bunce, Emily, and Robert Heine. “Swelling during Late Pregnancy.” Merck Manual, July 2023, www.merckmanuals.com/home/women-s-health-issues/symptoms-during-pregnancy/swelling-during-late-pregnancy.

Mayo Clinic Staff. “Pregnancy Weight Gain: What’s Healthy?” Mayo Clinic, 19 Dec. 2024, www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy-weight-gain/art-20044360.

“Pregnancy: Second Trimester.” Cleveland Clinic, 26 Sept. 2024, my.clevelandclinic.org/health/articles/16092-pregnancy-second-trimester.

“The Second Trimester.” John Hopkins Medicine, 2020, www.hopkinsmedicine.org/health/wellness-and-prevention/the-second-trimester.

“Week 12.” NHS.UK, 13 June 2023, www.nhs.uk/start-for-life/pregnancy/week-by-week-guide-to-pregnancy/1st-trimester/week-12/.

“Week 15.” NHS.UK, 13 June 2023, https://www.nhs.uk/start-for-life/pregnancy/week-by-week-guide-to-pregnancy/2nd-trimester/week-15/.

About the Author Krista Ruffo, born, raised, and still living in Orlando, Florida, began blogging with South Project in February of 2025. She’s a UCF alum with a BA in English and a Certificate in Editing and Publishing. A passionate writer and reader, Krista aspires to work in book publishing in the future. She currently works as a Content Coordinator for a family magazine. In her free time, she enjoys writing poems, taking photos, making art, hiking, and gardening.