Week 13 of Pregnancy: A Lemon, and the Start of the Second Trimester

Week 12 was the milestone of finishing the first trimester. Week 13 is where the second trimester actually begins — and for a lot of women, it’s the point where pregnancy starts to feel a little less like something you’re enduring and a little more like something you’re living with.

What’s actually happening in your body

The baby is now around 7.4cm long, roughly the size of a lemon. Internally, the ovaries or testes are now fully developed, and the finishing touches are being made externally. Movements are becoming more intentional rather than random, and some babies even begin sucking their thumb at this stage, which helps develop the sucking reflex they’ll need after birth, according to NHS guidance on week 13 of pregnancy. Physically for you, a small bump may already be visible as the uterus grows upward and outward, and if you’ve been dealing with frequent urination, that often eases now as the uterus shifts away from the bladder.

What I actually felt

I was fortunate not to have major symptoms through the first trimester, but a few smaller physical changes did show up — one of the more distinctive ones was wanting to eat quite late at night. My husband was consistently good about it, cooking something light for me on those evenings, and often eating with me rather than leaving me to it alone. I also noticed some mood swings starting around this time, though they stayed fairly manageable rather than anything overwhelming.

If you’re noticing odd-timed hunger or mood shifts entering the second trimester, that’s a normal continuation of pregnancy’s hormonal changes — it doesn’t stop just because the first trimester technically has.

Nutrition focus this week

If late-night hunger is showing up for you too, a light, easy meal in the evening is a reasonable way to handle it rather than ignoring it or overcompensating with something heavy. Beyond that, the fundamentals stay the same — consistency with your prenatal vitamin and the guidance in our foods and drinks to limit or avoid during pregnancy.

What to discuss with your doctor or midwife

If you’ve noticed mood swings that feel like more than “mild” — persistent low mood, anxiety that doesn’t ease, or anything that’s affecting your day-to-day life — mention it at your next appointment rather than assuming it’s just something to push through. Most mood changes in pregnancy are ordinary hormonal fluctuation, but it’s always worth flagging anything that feels like more than that.

Frequently asked questions

Do first-trimester symptoms really ease by week 13?

For many women, yes — nausea and extreme fatigue commonly start improving as the second trimester begins, though the exact timing varies. Some symptoms, like mood swings or appetite changes, can continue well beyond the first trimester.

Is it normal to want to eat at unusual times, like late at night?

Yes. Appetite and hunger patterns can shift throughout pregnancy, and odd timing doesn’t need a specific explanation — a light snack or meal when you’re genuinely hungry is a reasonable response.

Should I be worried about mood swings this far into pregnancy?

Mild, manageable mood swings are common well into the second trimester and aren’t a cause for concern on their own. If they feel severe or persistent, that’s worth raising with your doctor or midwife.

Is a visible bump normal at week 13?

Yes, for some women — it varies by body type and whether it’s a first pregnancy. A small, genuine bump at this stage is common, though plenty of women don’t show noticeably until later.

Why does the need to urinate frequently often ease around now?

As the uterus grows, it moves upward and away from the bladder, reducing the pressure that caused frequent urination earlier in the first trimester.

References

1. NHS — Your Pregnancy and Baby Guide, Week 13. nhs.uk