The third trimester runs from week 27 to week 40. It is the home straight, and it does something odd to your sense of time. The weeks feel like they should go fast. You are nearly there. But they also feel slow in a way that is hard to explain until you are in it.
The second trimester is often described as the comfortable phase. This one is different. The pregnancy is fully visible, the due date is real, and both of you are living with a level of anticipation that sits somewhere between excitement and anxiety.
This is the phase where being present and practical matters most.
What is happening in the third trimester
Between week 27 and week 40, the baby goes from roughly 900 grams to somewhere around 3 to 3.5 kilograms. That rapid growth is what drives most of the physical changes your partner experiences.
The baby’s lungs are maturing. The brain is developing at pace. Fat is accumulating under the skin. By around week 34, most babies are in a head-down position in preparation for birth. By week 37, the pregnancy is considered full term.
There is a lot happening, even in the final weeks when it might look from the outside like things have slowed down.
What your partner is likely experiencing
The physical discomfort of the third trimester is real, and it is different from earlier in the pregnancy.
Back and hip pain. The bump is significant now, and carrying that weight for weeks takes a toll. Back pain is very common and can disrupt sleep, movement, and daily life.
Disrupted sleep. Sleeping with a large bump is genuinely difficult. Comfortable positions become limited. The baby may be most active at night. Your partner is likely waking multiple times and not getting the rest they need.
Braxton Hicks contractions. These practice contractions are normal and usually painless, but they can be unsettling, especially closer to the due date when it becomes harder to tell them apart from early labour.
Shortness of breath. As the baby grows upward, there is less room for the lungs to expand fully. Breathlessness on mild exertion is common.
Nesting instinct. Many people feel a strong urge to organise, prepare, and sort things out as the due date approaches. If your partner is suddenly driven to reorganise the house or get everything in order, this is normal. It is worth taking seriously rather than dismissing.
Emotional intensity. The third trimester brings its own emotional weight. Excitement, fear about the birth, anxiety about becoming a parent, and a kind of grief for life as it has been. These feelings are real and often mixed together.
Appointments become more frequent
In the third trimester, antenatal appointments shift from monthly to every two weeks, and then weekly in the final stretch. There is more to monitor at this stage.
Around week 36, the midwife or doctor will check the baby’s position, assess size, and begin preparing for the final approach. If the baby is not head-down by this point, options may be discussed.
These appointments matter, and being there when you can shows that you are engaged. Your partner is carrying a lot. Showing up to appointments is one of the most concrete ways to share the weight.
Getting the practical things done
The third trimester is when the conversations you may have been putting off need to happen.
Hospital bag. Most guidance suggests having it ready by week 36. You do not need to overthink it, but having it packed matters. Labour can start earlier than expected.
Parental leave. If you have not finalised your leave arrangements, now is the time. Knowing the plan reduces stress for both of you in the final weeks.
Birth preferences. This does not have to be a detailed written plan, but having a conversation about what your partner wants, what they are anxious about, and how you can best support them during labour is important. You cannot control what happens, but you can know what matters to them.
The logistics. How are you getting to hospital or the birth centre? Is there anything that needs sorting before the baby arrives? The mental load of these questions is real. Taking ownership of them, rather than waiting to be asked, makes a difference.
The last few weeks
The final stretch, roughly weeks 37 to 42, has its own particular quality. The due date is circled on the calendar, but babies arrive on their own schedule. The window can feel long.
Your partner may be uncomfortable, impatient, anxious, and ready. The combination is a lot to hold. This is a time for patience, for being present without adding pressure, and for letting your partner lead on what they need.
The waiting is part of it. So is the uncertainty. Most partners find that staying close, staying calm, and keeping things as normal as possible is more useful than filling the space with anxiety.
What comes after
The third trimester ends when the baby arrives, which can happen anywhere from week 37 to week 42 or a little beyond. The due date is an estimate, not a deadline.
What you do know is the week. That matters for appointments, for conversations with your partner, and for your own sense of where you are in the journey. If you want to follow the full arc from the beginning, the guides for the first trimester and second trimester are worth reading alongside this one.
The third trimester is the most intense. It is also the final one. Showing up well here is one of the most important things you can do as a partner.