The foetus is now 65mm — a lemon — and the development this week comes with one of the most charming details in the whole of pregnancy: your baby is sucking their thumb. Not as a deliberate, conscious act, but as a reflex — the same rooting and sucking reflexes noted last week are already being exercised, already preparing the muscles and the coordination that will be needed in the first minutes after birth when your baby needs to feed.
The uterus has risen above the pubic bone this week — a quiet anatomical milestone that marks the move from the pelvis to the abdomen. For most people this is not yet externally visible, but the fundus (the top of the uterus) is now palpable just above the pubic bone. The bump that will define the second and third trimesters is beginning its journey upward.
The foetus's bone development continues at pace — the soft cartilage of the earlier weeks is steadily hardening into proper bone, a process that will continue for years after birth. The intestines, which temporarily protruded into the umbilical cord in the early embryonic stage, have fully returned to the abdominal cavity and are now settled in their permanent positions. The foetus is beginning to develop a unique pattern of movements — some babies are active and wriggly at this stage; others are calmer. This individuality, already present, will only become more apparent over the coming weeks.
My midwife told me about the thumb-sucking at my 16-week appointment and I couldn't stop thinking about it. That specific gesture — so human, so familiar — happening in there without me knowing. I started looking at babies' hands differently after that. At the scan you could almost see it.
The physical transition into the second trimester is, for most people, one of the most welcome experiences of the whole pregnancy. Not always instant — some people continue to feel nauseous for another two or three weeks, and some for longer — but for the majority, week 13 is when the worst of the first trimester symptoms begin to lift in earnest. The physiological reason is now well established: hCG has plateaued and is declining, progesterone is stabilising, and the placenta has fully taken over.
The exhaustion that has been a constant companion since around weeks 5 or 6 often improves considerably in the early second trimester. Not completely — growing a baby never stops being metabolically demanding — but the quality of the tiredness changes. The bone-deep, compelling fatigue of the first trimester tends to give way to something that responds better to rest and is manageable alongside ordinary life.
Energy — often increases noticeably. Many people describe the second trimester as the period when they finally feel capable of doing things again — exercise, social plans, work at full capacity.
Appetite — typically returns, sometimes enthusiastically. The body is also beginning to make genuinely increased nutritional demands: iron, calcium, and protein requirements all rise in the second trimester. Eating well — varied, nutrient-dense food — matters more from now on than the first trimester's survival eating.
Skin and hair — many people notice improved hair thickness and either clearer skin or a continued glow from the expanded blood volume. The 'pregnancy glow' is most commonly reported in the second trimester.
One new physical experience to be aware of in the second trimester: Braxton Hicks contractions — painless tightening of the uterus that can begin from around week 13, though most people don't notice them until later. They are the uterus practising for labour: irregular, brief, and not accompanied by any other symptoms. They differ from labour contractions in that they are irregular, do not intensify, and stop when you change position or activity. If you experience regular, painful tightening, contact your midwife.
The emotional shift of week 13 is real, but it doesn't always arrive as cleanly as the calendar suggests. For those who have spent the first trimester in a state of suspended anxiety, the permission to relax does not always switch on the moment the trimester ends. Caution that has become habitual takes time to unlearn. If you find yourself still holding your breath slightly, still waiting for something to go wrong, this is entirely normal — you are de-escalating from weeks of sustained vigilance, and that has its own timeline.
For most people, though, week 13 brings a genuine shift in how the pregnancy feels to inhabit. The scan has happened. The circle of people who know has expanded. The symptoms are easing. The bump — not yet visible to others, but increasingly present to you — is beginning to feel like a physical confirmation rather than just a hormonal fact.
I turned thirteen weeks on a Tuesday and woke up feeling better. Not completely better, but a different kind of not-completely-better. Like the fog had lifted enough to see through it. I ate breakfast and it tasted like something. I remember thinking: oh. This is what it's going to be like now. That was a very good Tuesday.
The second trimester is also the period when many people begin, for the first time, to think about and plan for the baby rather than simply trying to get through the pregnancy. Antenatal classes, nursery arrangements, telling wider circles of people, thinking about names and birth preferences — the second trimester is when these conversations become available in a way they couldn't quite be in the first. Give yourself permission to enjoy them.
If the shift doesn't feel as dramatic as anticipated — if you are still anxious, still struggling, still not finding it easier — please speak to your midwife or GP. Antenatal anxiety and depression don't resolve automatically at twelve or thirteen weeks, and if you are still finding the emotional experience of pregnancy very difficult, you deserve support. The second trimester being the 'golden period' is a pattern, not a prescription.
The second trimester opens new territory — here are the guides most relevant to where you are now.
The second trimester is often described as the period when pregnancy becomes enjoyable for partners as well as the pregnant person. The anxiety of the first trimester eases, the physical demands on your partner begin to lessen, and the pregnancy starts to become visible and tangible in ways that the first trimester — largely invisible and privately suffered — couldn't be.
The practical texture of the relationship shifts this week too. The food adaptations, the patience with unpredictable nausea, the covering for someone who was too exhausted to be present — all of this begins to ease. What replaces it is different: conversations about the future, beginning to plan, a pregnancy that increasingly exists in the world rather than just between the two of you.
- The bump is coming. Over the next few weeks your partner's body will begin to change visibly. Some people feel joyful about this; others have complicated feelings about it. Follow your partner's lead in how they talk about their changing body — your enthusiasm and their ambivalence can coexist without either needing to match the other.
- Think about antenatal classes together. The popular ones book up months in advance. Weeks 13–16 is the right time to research options and put your name down. NHS, NCT, and independent options all vary in what they cover and how they run — choosing together means you're both committed.
- The 16-week appointment is the next antenatal contact. It is a shorter appointment than the booking, but it is a good moment to attend together if you can — it is when the anomaly scan (week 18–20) is typically discussed and booked.
Research and book antenatal classes. This is the single most valuable practical action of the early second trimester, and the one most commonly left too late. The good classes fill up four to six months before the baby is due — which means if your due date is around 40 weeks and you're currently at 13, you have a narrower window than it might seem.
NCT classes — widely regarded, partner-inclusive, with an emphasis on birth options, feeding, and the postnatal period. Paid, with means-tested bursaries available. nct.org.uk to find local options.
Independent classes — hypnobirthing instructors, independent midwives, and others offer a range of options. Worth researching locally — some are excellent and more flexible than structured programmes.
Online courses — useful, particularly for covering knowledge gaps and for partners who can't attend in-person sessions. Not a full substitute for the group experience of in-person classes, which provides peer connection as well as information.
At your 16-week appointment — now approaching — this is worth raising:
The guidance for the second trimester differs from the first in a few meaningful ways — iron and calcium become particularly important, caffeine limits remain relevant, and there are some foods and activities that remain relevant to check. Getting a clear, personalised answer from your midwife — rather than trying to piece together advice from various sources — is worth the two minutes the question takes at the appointment.