Fetal Development: Week 13

Size

Lemon

Length

2.9 in (7.4 cm)

Weight

0.81 oz (23 g)

Trimester

1st

Welcome to the end of the first trimester! Your baby is the size of a lemon. The placenta is now fully in charge of hormone production, and the risk of miscarriage has significantly dropped.

Key milestone: The baby's vocal cords form. The placenta is fully functional. Intestines move into the abdomen.

What's happening this week

At week 13, your baby measures 2.9 in (7.4 cm) and weighs approximately 0.81 oz (23 g) — about the size of a Lemon. All major organs are forming or have formed, and the foundation for a healthy pregnancy is being established. This rapid growth is why tracking fetal development week by week is so exciting for expecting parents.

How to bond this week

Start talking to your baby even though they can't hear you yet — your voice will become familiar over time. Consider starting daily voice notes with Baby Whispers to build the habit early.

Common questions about fetal development at week 13

Parents at week 13 often ask how their baby is developing and what to expect at the next prenatal visit. Your healthcare provider will monitor growth through fundal height measurements and ultrasounds. Meanwhile, tracking fetal development week by week helps you understand the incredible transformations happening inside.

Looking ahead: what changes at week 14

Next week, your baby's development continues as they grow larger and more complex. Each week builds on the last, and the changes you're noticing now are preparing your baby for the milestones ahead. Baby Whispers evolves with each week too — our daily voice notes reflect your baby's changing world.

Prenatal Care at Week 13

Depending on where you are in your pregnancy, your prenatal appointments will focus on different aspects of care. Early appointments confirm the pregnancy, establish your due date, and include blood work, urine tests, and sometimes an early ultrasound. Your provider will discuss prenatal vitamins, lifestyle adjustments, and what to expect in the coming weeks.

Your baby at week 13 — the size of a Lemon — is developing exactly as expected. Tracking fetal development week by week helps you feel connected to the incredible process unfolding inside you.

Hear your baby's voice at week 13

Imagine waking up to a voice note that sounds like your Lemon-sized little one.

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