Day 4 baby development and maternal changes
Currently week 1 (preconception stage): medical gestational age counts from the first day of your last menstrual period. At weeks 1–2 you are not yet pregnant; below is guidance on follicle development, uterine lining preparation, and preconception.Learn the full BPD/AC/FL reference table for weeks 14–42 →
Today's key focus
Exercise moderately: walk 20-30 minutes or do a gentle yoga class to stay active and relaxed. Pregnancy exercise improves metabolism, lowers blood pressure, reduces anxiety and builds a foundation for the months ahead. If you do not usually exercise, start with 10 minutes a day and build up. During the preconception phase, avoid high-intensity exercise — too much can affect ovulation and cycle regularity.
What your baby is doing today
Fallopian tube cilia move rhythmically, building a passageway for future egg pickup and gamete transport.
Pregnancy progress
Day 4 / about 280 days. Progress 1%
Note: week 1 is the preconception stage, not yet pregnant; there is no fetal weight/length yet, so this stage focuses on follicle development, uterine lining preparation, and preconception guidance.
This week (week 1) development overview
- Pregnancy is counted from the first day of your last menstrual period; you are not yet truly pregnant, and medicine uses the last period as the most reliable starting point
- Rising estrogen thickens the uterine lining (functional layer), preparing a fertile bed for a fertilized egg
- Under follicle-stimulating hormone (FSH), a batch of antral follicles in the ovaries is recruited and begins to develop
- Usually only one follicle becomes the dominant follicle; the others gradually regress
- Uterine glands proliferate and blood vessels increase, with richer blood flow to nourish the future embryo
- Cervical mucus gradually thins after your period to help sperm pass through
- The pituitary-ovarian axis activates, with estrogen and a small amount of progesterone jointly regulating the cycle
- Granulosa cells of the follicle secrete estrogen, finely regulating FSH and LH via negative feedback
- Primary oocytes have been waiting in the ovary for years; this cycle reserves them for future ovulation
- Basal body temperature is in the low phase; after ovulation it will rise 0.3-0.5°C because progesterone rises
- Fallopian tube cilia and movement prepare for future egg pickup and transport of the fertilized egg
- If conception succeeds, the ruptured follicle forms the corpus luteum, which secretes progesterone to maintain the lining
This week's key concerns
Maternal body changes this week
- Your last period has just ended or is still ongoing, and you feel no different than usual
- Some cramps or lower-back soreness are normal menstrual reactions
- Basal body temperature is in the low phase and only rises 0.3-0.5°C after ovulation
- If cycles are regular you are in the follicular phase, with estrogen rising slowly
- Some people have mood swings or breast tenderness before or during their period, which ease as it ends
- There are no pregnancy symptoms at this stage; your body is preparing for conception
- The vagina is normally mildly acidic, which can inhibit bacteria; around ovulation the pH fluctuates slightly with hormones
- Energy and appetite are usually normal, making this a good time to adjust your routine for conception
Nutrition advice this week
From the preconception period, supplement folic acid 400-800μg daily through week 12 of pregnancy to help prevent neural tube defects. Key nutrients: ①Folate (leafy greens, legumes, animal liver; 400-800μg/day) ②Iron (red meat, spinach, dates — build iron stores) ③Iodine (iodized salt, kelp and seaweed; pregnancy needs about 230μg/day, higher than the 120μg for non-pregnant adults) ④Vitamin D (15-20 min of sun, egg yolk, mushrooms) ⑤Zinc (oysters, lean meat, nuts — supports egg quality) ⑥DHA (oily fish twice a week or algae oil). Also keep caffeine under 200mg/day, avoid alcohol and smoking, and limit cold-raw foods.
Spinach is rich in folate and iron, and eggs provide high-quality protein — a simple, nutritious preconception meal.
Prenatal education this week
There is no strong evidence that special prenatal stimulation makes a baby smarter during the preconception phase; the key is helping the mother relax and keep her endocrine system stable. You can do this: ①Relaxation: 10-15 minutes daily of deep breathing, meditation or gentle yoga to help lower cortisol; ②Environment: keep a regular routine, and stay away from smoke, alcohol, high heat and secondhand smoke to give the future embryo a stable internal environment; ③Emotional connection: plan together with your partner and keep a mood journal to reduce preconception anxiety; ④Light music: soft, calming white noise before bed to help you sleep. The best prenatal care at this stage is a healthy, stable maternal body.
Partner's tasks this week
①Do preconception checkups and genetic counseling with your partner (TORCH, blood count, thyroid function, etc.); ②Also quit smoking and alcohol, keep a regular routine and healthy diet (sperm production takes about 2-3 months, so adjusting early helps); ③Proactively learn about preconception health and build a warm, low-stress family atmosphere; ④Help record your partner’s last period date and assist with estimating ovulation and the due date.
Checkup reminders
If you are planning a pregnancy, we recommend preconception screening first: for the woman — blood count, blood type, liver/kidney function, thyroid function, TORCH (e.g. toxoplasmosis) and a gynecological ultrasound; for the man — a semen analysis. Both parties should take folic acid for 3 months in advance and quit smoking and alcohol. To find the fertile window, combine ovulation test strips, basal body temperature and cervical mucus; have intercourse every other day during the fertile window. Only do an early pregnancy test once pregnancy is suspected (delayed period); no need for frequent early testing.
Signs that need immediate care
The preconception phase has few true red flags, but see a doctor if any of the following occurs: ①abnormally heavy periods or periods lasting over 7 days, or severe cramps affecting daily life; ②abnormal bleeding outside your period or contact bleeding; ③long-term irregular periods, amenorrhea, or hormone imbalance affecting conception; ④regular sex without contraception for 1 year (6 months if over 35) without pregnancy — see a fertility specialist; ⑤persistent lower-abdominal pain or fever with abnormal discharge (watch for pelvic inflammatory disease); ⑥uncontrolled thyroid problems (palpitations, feeling cold, fatigue) — not ideal for pregnancy; ⑦severe anemia (dizziness, weakness) — treat it first; ⑧taking a teratogenic drug or being exposed to radiation — consult your doctor.
Week 1 frequently asked questions
Q: Why does week 1 count as part of pregnancy?
A: In medicine, pregnancy is counted from the first day of the last menstrual period, before actual conception. This is because the exact time of ovulation and fertilization is hard to pinpoint, so the last period is used as the most reliable starting point.
Q: How do I estimate my due date from my last period?
A: The most common method is Naegele’s rule: first day of last period + 280 days (40 weeks); you can also subtract 3 from the month (or add 9) and add 7 to the day. For example, a period starting February 1 gives a due date around November 8. If your cycles are irregular, an early ultrasound to check the dates is more accurate.
Q: How do I figure out my gestational age if my periods are irregular?
A: The last-period method is unreliable for irregular cycles. The most reliable approach is an ultrasound early in pregnancy (especially 6-8 weeks) using the crown-rump length (CRL) to verify dates; your doctor will adjust the due date accordingly.
Q: How long before conception should I quit smoking/drinking and take folic acid?
A: Start at least 3 months before pregnancy: take folic acid 400-800μg daily to help prevent neural tube defects, and both partners should quit smoking and alcohol (sperm production takes about 2-3 months, egg maturation about 3 months). If possible, do preconception screening first.
Q: What should both partners get checked before conception?
A: Woman: blood count, blood type, liver/kidney function, thyroid function, TORCH, gynecological ultrasound, cervical cancer screening. Man: semen analysis. Add tests as your doctor advises based on your history.
Q: Until when and how much folic acid should I take?
A: 400-800μg daily, from 3 months before conception through week 12 of pregnancy (the critical neural tube closure period); some higher-risk people are advised to continue the whole pregnancy.
Q: How do I know if I have ovulated?
A: Ovulation test strips detect the LH surge, basal body temperature rises 0.3-0.5°C after ovulation, and cervical mucus becomes clear and stretchy (egg-white-like). Ultrasound follicle tracking is the most accurate.
Q: Which day is easiest to conceive?
A: The fertile window is from 5 days before ovulation to 1 day after; intercourse 1-2 days before ovulation has the highest conception rate. Sperm can survive 3-5 days in the body.
Q: Is ovulation bleeding normal?
A: A tiny amount of pink-brown discharge lasting 1-2 days with no pain is usually a normal result of hormone fluctuation. If it is heavy, bright red, or comes with abdominal pain, see a doctor.
Q: How soon after sex can conception/ implantation happen?
A: Once inside, sperm can meet the egg within hours to days; the fertilized egg generally implants 6-10 days after fertilization. So testing immediately after sex is meaningless.
Q: When is the best time to take a pregnancy test?
A: First-morning urine 1-2 days after a missed period is fairly reliable; blood hCG can be detected as early as about 7-10 days after fertilization. Testing too early often gives false negatives.
Q: Can I drink coffee while trying to conceive?
A: Caffeine is recommended at no more than 200mg/day (about one medium black coffee). Excess caffeine is associated with a slightly lower conception rate, so cutting back is advisable.
Q: Can I exercise before conception?
A: Yes, and it is recommended: walking, prenatal yoga and swimming all work well. Avoid intense exercise and high-heat environments, and keep a moderate weight to support ovulation.
Q: How soon can I get pregnant after stopping the pill?
A: For combined short-acting oral contraceptives you can start trying 1 month after stopping; for long-acting injections, about 6-12 months is advised. Consult your doctor before trying.
Q: What to watch for when trying at 35+ (advanced maternal age)?
A: Do a full preconception assessment (ovarian reserve AMH, thyroid function), start trying early, and see a fertility specialist if nothing happens in 6 months; take folic acid and manage chronic conditions.
Q: Do I need DHA and vitamin D before conception?
A: DHA supports early neural development — you can eat low-mercury fish twice a week or use algae oil; vitamin D supports calcium absorption and immunity — if you get little sun, supplementation can be considered under your doctor’s guidance.
Q: Is ovulation pain normal?
A: Brief mild discomfort on one side (mittelschmerz) is often normal. If it is severe, persistent, or comes with bleeding or fever, see a doctor to rule out ovarian cysts or pelvic inflammatory disease.
Data sources & notes
- Guidelines for Pre-conception and Prenatal Care (Chinese Society of Obstetrics and Gynecology)
- ACOG Methods for Estimating the Due Date (Committee Opinion No.700)
- WHO INTERGROWTH-21st fetal growth standards
This tool provides algorithm-based estimates from the authoritative standards above for pregnancy time planning and general reference. It does not replace a doctor's diagnosis or individualized medical advice; follow your obstetrician for all prenatal care decisions.
View the full fetal BPD/AC/FL reference table (weeks 14–42) →
Data note: BPD, AC, and FL reference values follow the median and 3rd–97th percentile ranges of the Expert Consensus on Fetal Biometric Ultrasound Reference Values (2024). For pregnancy education and everyday reference only; does not replace professional ultrasound diagnosis. When shown, today's weight/length are interpolated estimates from week-to-week data.