Lesson 1 · The Pregnancy Clock

Everything in the next nine months is scheduled against a number: how many weeks pregnant she is. Scans, tests, deadlines, your leave, the moment you're allowed to panic about the hospital bag. Get the clock wrong and every date downstream is wrong. So this is lesson one.

1. Two clocks, two answers

You got two numbers because two different things were being measured.

Clock	Starts counting from	Who uses it
Gestational age	First day of her last period	Every midwife, doctor, scan, app, book, and form in the NHS
Conception age	The day the egg was actually fertilised	Home test "conception indicators", and basically nothing else

Ovulation — the release of the egg — happens roughly two weeks after a period starts. So conception is about two weeks into the gestational clock. Which means:

The conversion

Conception weeks + 2 = gestational weeks. Your test said 1–2 weeks since conception. The doctor said 3–4 weeks pregnant. These are the same statement. Nobody is wrong.

The oddity you have to swallow: on the clock that everyone actually uses, she was counted as "pregnant" for a fortnight before there was anything there. It's not a biological claim, it's a bookkeeping convention — the first day of a period is the one date you can reliably know, and ovulation isn't. Medicine picked the measurable landmark over the meaningful one.

From here on, use gestational weeks only. When she says "I'm eight weeks", when an app says "week 12", when a form asks for gestation — it is always this clock. Mentally bin the conception number; it has done its one job.

2. Where you actually are

Her last period began 2 August 2026. A pregnancy is dated as 40 weeks from that day, so the arithmetic is now exact:

4+0

Gestational age on 30 Aug 2026

9 May

Estimated due date, Sunday 9 May 2027

36 wks

Left to run from today

That is a solid estimate — a known period date is the input the whole system is designed around. It still gets confirmed or adjusted — properly and officially — at the dating scan around 11–14 weeks (late October). The sonographer measures the foetus crown-to-rump and the machine issues an EDD. That date becomes the truth: every subsequent appointment is booked off it, and it overrides both the app and the arithmetic.

Due dates are an estimate, not an appointment. Only about 1 in 25 babies arrives on the predicted day; "term" is anything from 37 to 42 weeks. When people ask you the due date, the honest answer is a fortnight, not a Tuesday.

3. The whole map, in one screen

Front-loading the shape of it, so nothing arrives as a surprise. Dates assume a mid-May due date and will shift after the dating scan.

Week	What happens	Roughly when
now–10	Self-refer to NHS maternity. You do this, not your GP.	Sept 2026
8–12	Booking appointment. ~1 hour with a midwife. Bloods, BP, history, plan.	late Sept–Oct
11–14	Dating scan. First picture. Official EDD. Optional screening for three chromosomal conditions.	late Oct
16	Midwife check. Screening results discussed.	Nov
18–21	20-week scan. The detailed anatomy scan. You can find out the sex here.	Dec
24–28	Gestational diabetes test if she's higher-risk. Bloods again at 28.	Jan–Feb 2027
25, 31	Extra checks — first babies only. Birth preferences discussed.	Jan / Mar
34–41	Appointments every 2 weeks, then weekly. Baby's position tracked from 36.	Mar–May
37–42	"Term." Any arrival in this window is normal.	18 Apr–23 May

A first pregnancy gets at least 10 appointments and 2 scans on the NHS; second-time parents get 7. You have the right to attend, and — if you're employed — the right to unpaid time off for two of them.

Full printable version: Reference · NHS Antenatal Timeline. Terminology you'll hit today: Reference · Glossary.

4. What has to happen now

Four things. Two are urgent, in the sense that delay costs something real.

Today · urgent Folic acid, 400 micrograms daily Cuts the risk of neural tube defects like spina bifida. The neural tube closes by week 7 — so this window is closing now, not later. Continue to 12 weeks. Any pharmacy, a few pounds. Plus vitamin D, 10 µg daily.
This week Self-refer to NHS maternity services In most of England you no longer go via the GP — you fill in a form on the NHS site and the trust contacts you. The booking appointment should happen by 10 weeks, and slots go. Do it here.
This week Agree the three "no" list No alcohol. Caffeine capped at 200 mg/day (~two mugs of instant, or one strong filter coffee). No smoking, including yours near her. Everything else — the cheese, the cured meat, the runny eggs — is a longer list you'll learn from the food safety card.
Before ~week 12 Decide who you tell, together Most people wait until after the 12-week scan, because miscarriage risk drops sharply past that point. But that convention means many couples go through the hardest weeks with nobody to lean on. It is a choice, not a rule — and it's hers to lead. Your job is to ask what she wants and then hold the line with your own family.

Worth knowing now, not later

Roughly 1 in 5 confirmed pregnancies ends in miscarriage, the overwhelming majority in the first 12 weeks, and almost never because of anything either of you did. Once a heartbeat is seen at 6–7 weeks the risk falls to about 1 in 10, and after 12 weeks it drops sharply. This is not written here to frighten you. It's written because the single most common failure of new fathers-to-be is being blindsided — and because if it happens, "we did something wrong" is the reflex, and it is almost always false.

Check yourself

Don't scroll back. Answer from memory — getting one wrong and being corrected is worth more than getting it right by looking.

Retrieval practice

An app reports "3 weeks since conception". What would the midwife call this?

Conception weeks + 2 = gestational weeks. The clinical clock starts two weeks earlier, at her last period.

Which date is the one the NHS will treat as authoritative?

The 11–14 week dating scan measures the foetus directly and issues the official EDD. Everything before it is provisional.

By what gestational week should the booking appointment have happened?

The NHS target is a booking appointment before 10 weeks, and always before the dating scan. Self-refer now to get a slot.

Why is folic acid urgent rather than merely important?

It protects a structure that has finished forming by about week 7. Starting in month three is starting after the event it prevents.

Free recall — harder, and worth more. Without looking: write the four scheduled milestones between now and the new year, with roughly which week each falls in.

Booking appointment (8–12 weeks, ~1 hr with a midwife) · Dating scan (11–14 weeks — official due date, optional screening) · 16-week midwife check (screening results) · 20-week anatomy scan (18–21 weeks — the detailed one; sex, if you want it). Close but not exact is a pass. Vague is a re-read.