You are 15 weeks and 6 days

To help your baby's lungs expand and develop ready for breathing, the chest wall must be fully surrounded by amniotic fluid.

169 days until your due date

Your baby's lungs keep branching and dividing. The cells lining the airways constantly produce fluid, which leaves the lungs when your baby makes breathing movements, controlled by the vocal cords in the larynx.

The lungs also have glands that make mucus, and cells with tiny hair-like cilia have appeared to move it along. After birth, this mucus stops the constant flow of air from drying the lining of the lungs, traps dust, and acts as a barrier to infection.

Because the gut is still very immature and your baby doesn't swallow often yet, the amount of amniotic fluid gradually increases. By 37 weeks, your baby will swallow 1.75 pints (almost a liter) a day, half the total amniotic fluid.

Explainer

Soft ribs

Because the skin is almost transparent, the ribs are easy to see. They're still very soft and made mostly of cartilage.

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Relationships: Surprisingly sexy

You may be surprised by a sudden boost in your libido. In the second trimester, many women feel much more energetic and sexy. Extra blood flow to the pelvis and more vaginal lubrication mean that, in theory, sex can be better than ever.

High progesterone and estrogen make your breasts and vagina extra sensitive, so you may be aroused more easily and orgasm more quickly than usual. Your uterus tightens when you orgasm, so be prepared for that.

Your partner may be delighted, and enjoy your beautiful rounded body, but if he isn't responding positively, talk to him about how he feels.

This is general information based on NHS guidance, not medical advice, and every pregnancy is different. Talk to your midwife or GP about anything that worries you. If your baby's movements slow down or change, or you have bleeding, severe pain or leaking fluid, call your maternity unit straight away. In an emergency, call 999.