How Accurate is a Pregnancy Calculator?
A pregnancy calculator is quite accurate for giving an estimated timeline of your pregnancy, especially in
the early weeks. It follows the same basic formula that doctors use to calculate pregnancy dates. However,
it is important to understand that the result is an estimate, not an exact prediction.
A pregnancy calculator works best for women with regular menstrual cycles, as it usually calculates the due
date by counting 40 weeks from the first day of the last menstrual period (LMP). When used correctly, it
gives a clear idea of your due date, pregnancy week, and trimester.
However, it is said that the
due date may not
always be exact.
Ovulation can happen earlier or later than expected, periods may be irregular, and every baby grows at a
different pace. For women who conceived through IVF or fertility treatments, a different calculation
method is used, which can be more precise because the exact transfer date is known.
What Happens in Pregnancy Each Week & Trimester?
Pregnancy is usually divided into weeks and three trimesters to help track your baby’s growth and understand
the changes happening in your body. Here’s a simple breakdown of what happens in each week of pregnancy.
First Trimester (Weeks 1–12): The Starting of Life
Weeks 1–4
Fertilisation and implantation occur during this period. The embryo begins to form, and by the end of
week 4, the placenta starts developing. You may notice a missed period and early symptoms like fatigue
or mild cramping.
Tip: It is important to start taking prenatal vitamins with folic acid, eat healthy meals, and avoid
alcohol, smoking, or excess caffeine.
Weeks 5–8
During the 5th week, the baby’s heart begins to beat, and tiny facial features start to emerge. Early
development of the brain, spinal cord, and organs takes place. The mothers might experience nausea,
breast tenderness, and tiredness.
Tip: Eating small, frequent meals, staying hydrated, and resting when possible can help manage these
symptoms.
Weeks 9–12
Baby’s major organs, muscles, and nerves continue developing during these weeks. By the end of week 12,
the embryo is officially called a fetus. Mother may experience mood swings and bloating.
Tip: It is essential to maintain good posture, avoid heavy lifting, attend the first prenatal check-up,
and continue eating balanced meals.
Second Trimester (Weeks 13–27): Growth and Movement
Weeks 13–16
The fetus grows rapidly, facial features and limbs become more defined, and bones begin to harden.
Mother may experience less morning sickness and her energy levels improve.
Tips: Comfortable clothing, gentle exercises like walking or prenatal yoga, and continued prenatal
vitamins help you stay healthy.
Weeks 17–20
Movements may be felt for the first time, and the baby’s sex can often be identified via ultrasound.
Mothers may notice backaches, leg cramps, or mild swelling.
Tip: Maintaining good posture, eating iron-rich foods, and monitoring fetal movements are helpful
practices.
Weeks 21–24
The baby’s senses continue developing, and they may respond to sounds and light. False labour pain and
contractions might start, and stretch marks can appear.
Tip: Staying hydrated, moisturising skin, attending scans, and wearing supportive footwear can help
manage physical changes.
Weeks 25-27
The fetus gains more weight, and organs continue maturing. Mothers may notice increased fatigue and
minor discomfort.
Tip: Gentle activity, short walks, balanced meals, and proper rest are important during these weeks.
Third Trimester (Weeks 28–40): Preparation for Birth
Weeks 28–31
The baby grows rapidly, lungs and brain continue developing, and movements become stronger. Mothers may
experience swelling in the feet and ankles, back pain, and frequent urination.
Tip: Resting often, elevating legs, practising breathing exercises, and maintaining a nutritious diet
are essential.
Weeks 32–34
The baby’s bones are fully formed but soft, and the body continues to gain weight. Mothers may
experience shortness of breath, heartburn, and sleep disturbances, which are common.
Tip: Sleeping on the left side, avoiding heavy meals before bed, and tracking baby movements help ease
discomfort.
Weeks 35–37
The baby continues gaining weight, and lungs are almost fully developed. Mothers feel increased pelvic
pressure and stronger labour pain and contractions.
Tip: Preparing a hospital bag, discussing the birth plan with your doctor, and light activity like
walking keep you ready for labour.
Weeks 38–40
The baby is fully developed and ready for birth. The contractions may begin, the cervix softens, and
nesting instincts appear.
Tip: Staying calm, practising relaxation techniques, monitoring labour signs, and staying hydrated are
key steps to prepare for delivery.
Common Mistakes to Avoid While Calculating Pregnancy
Calculating pregnancy can seem simple, but there are several common mistakes that can lead to inaccurate
results. Being aware of these can help you get a more reliable estimate of your due date and pregnancy
weeks.
- Assuming a 28-day cycle : Ovulation may not occur exactly 14 days after your last period, so due
dates can be inaccurate.
- Incorrect last menstrual period (LMP) date : Entering the wrong start date or having irregular
cycles can skew results.
- Confusing implantation bleeding with a period: Mistaking early spotting for a period can change
the calculated pregnancy timeline.
- Using the LMP method for IVF pregnancies: IVF pregnancies require calculation based on the embryo
transfer date, not LMP.
- Ignoring personal factors: Irregular cycles, multiple pregnancies, or health conditions can
affect calculation accuracy.
Whether you conceived naturally or through IVF, using a pregnancy calculator gives you a clear understanding
of your pregnancy timeline and helps you plan doctor visits, scans, and prenatal care. While calculators
provide accurate estimates, it’s important to remember that ultrasound scans and expert guidance from
fertility specialists provide the most reliable information about your pregnancy.
Every pregnancy is unique, and personalised care is key for the best outcomes. If you want accurate
pregnancy tracking, guidance for IVF or natural conception, and expert support at every stage, our team at
Crysta IVF is here for you.
