20 weeks pregnant: fetal development

Until now, your baby has been measured from head (crown) to bottom (rump), but from this point on, she'll be measured from crown to heel. That's because her body is now in proportion.

This week, your baby measures about 25.6cm, or the length of a banana, and weighs about 300g (Hill 2019).

You're halfway to your due date and your baby is becoming more active every day. Even if you're still waiting to feel that exciting first kick, your baby is busy flexing and stretching (Moore et al 2019a). She's probably sucking her thumbs or fingers, too!

At your anomaly scan, which will take place between 18 weeks and 21 weeks, the sonographer will check how your baby's growing by measuring the circumference of her head and abdomen, and her thigh bone (femur) length (ASUM 2018). She'll measure your baby's head and body because it can be difficult to record your baby's length accurately when she's curled up (Loughna et al 2009).

A slick, fatty substance called vernix caseosa is beginning to form within the pores of your baby's developing skin (Moore et al 2019b, Singh and Archana 2008). In the third trimester, it will be secreted from her skin follicles to act as a moisturiser and lubricant, helping to protect her skin during from her long immersion in amniotic fluid (Singh and Archana 2008, NHS 2018, Taïeb 2018, Visscher et al 2015).

Vernix also plays a role in the transition from womb to world, by helping your baby's skin to adapt from a watery to a dry environment (Singh and Archana 2008, Visscher et al 2015). It may also help your baby stabilise her body temperature (Singh and Archana 2008) and fight infection (Singh and Archana 2008, Visscher et al 2015).

Check out our pregnancy guide to see what changes may happen to you at 20 weeks pregnant.