13 Weeks Pregnant — Baby Is the Size of a Lemon
At 13 weeks you are 91 days into the 40-week count, with 189 days to go and 33% of the pregnancy behind you. Baby is about the size of a lemon and weighs about 1.8 g. This page fixes week 13 in place: what is developing, which appointments are still ahead, and how the week maps onto months.
33% of 280 days. The due date itself is a midpoint, not a deadline: full-term births spread across roughly weeks 37 to 42.
This week
The vocal cords are forming and baby can open its tiny mouth. The odds of a healthy outcome lift dramatically here.
Measured in months, week 13 sits in month 3: The end of the first trimester brings the dating scan and the NT screening, and for many people the nausea starts to lift.
Appointments still ahead
| Window | Appointment | What it checks |
|---|---|---|
| 15–20 wks | Quad / anomaly blood screen | Optional blood test for screening risk factors. |
| 18–22 wks | Anatomy scan | Detailed look at baby's organs, limbs and growth — often the sex reveal. |
| 24–28 wks | Glucose tolerance test | Screens for gestational diabetes. |
| 28–34 wks | Routine growth checks | Regular midwife visits, bump measurements and blood pressure. |
| 34–36 wks | Group B strep swab | A simple swab that protects the baby during delivery. |
| 37–40 wks | Weekly checkups | Position checks, growth checks and the birth plan in earnest. |
Around week 13
| Week | Size | Weight |
|---|---|---|
| 12 | a lime | about 1.5 g |
| 13 | a lemon | about 1.8 g |
| 14 | a peach | about 2.4 g |
Frequently asked
What does 13 weeks pregnant mean in days and months?
13 weeks is 91 days since the first day of your last period, which is about 3 months pregnant on the four-week-per-month convention. 189 days remain in the 40-week count from here — that is 33% of the way through.
How big is a baby at 13 weeks?
Around the size of a lemon, at about 1.8 g. These are population averages: a scan measurement that differs by a few days is normal and does not by itself mean anything is wrong.
Which trimester is week 13?
The 2nd trimester. The split used here is the same one the calculator applies: the first trimester covers days 1–90, the second 91–195, and the third from day 196 onward. Other sources draw the boundary a week either side, which is why week 13 and week 14 can both be described as "end of the first trimester".
What appointments happen after week 13?
Next up: Quad / anomaly blood screen at 15–20 weeks, Anatomy scan at 18–22 weeks, Glucose tolerance test at 24–28 weeks. The full schedule is in the table above; exact timing varies by country and by your care team.