First trimester of pregnancy

Following ovulation, the egg cell travels through the fallopian tube, thus dividing into multiple identical cells to eventually form the blastocyst that attaches to the uterine wall (implantation), where it develops further until it becomes an embryo, then a fetus and, finally, a baby.

The period of pregnancy – which on average covers a span of 40 weeks – is counted from the date of the last menstruation, and is measured in trimesters, months, and weeks.

Finally, the third trimester covers the period from the 28th week to the date of delivery.

Although – both in Italy and abroad – the practice of measuring the period of pregnancy as described above is now consolidated, or according to the gestational method (which, in fact, measures the period of pregnancy starting from the date of gestation of the fetus), in some special cases the fetal method is still used

The fetal method refers to the fetal age (or age): in this case the duration of pregnancy is calculated starting from the first day following the presumed date of conception of the child and, therefore, is anticipated by 14 days compared to the gestational age.

The first trimester of pregnancy is the most important for the development of your future baby.

In this period the embryo (as the fetus is defined in its first 8 weeks of life) evolves up to weigh between 14 and 28 grams, and to be long on average between 7.5 and 10.5 centimeters.

Until the 20th week, the length of the embryo (and then the fetus) is usually measured from the head to the end of the spine. After that, its length is measured from head to toe.

The growth of the fetus in length will occur during the third, fourth and fifth months, and its weight gain will occur more during the last two months of gestation.

Until the middle of the first trimester of pregnancy, and especially in those pregnancies that have not been planned in advance, the small size and reduced weight of the fetus, mean that the future mother may not yet realize that she is carrying her future child.

Calendar of the evolution of pregnancy in the weeks of the 1st trimester

First month Second month Third month
1st and 2nd week 5th week 9th week
3th week 6th week 10th week
4th week 7th week 11th week
8th week 12th week
13th week

What are the most common symptoms-pregnancy in the first trimester

Generally, the first symptoms that accompany pregnancy are nausea, vomiting, frequent urination, extreme tiredness and exhaustion, breast soreness.

Many women begin to experience these symptoms, even before a missed period or a positive pregnancy test.

As gestation progresses, you may begin to experience other symptoms such as mood swings, headaches, cramps, constipation, indigestion, bloating, cravings or repulsion of foods, and an incredibly strong sense of smell, which often contributes to worsening nausea.

During this period, diarrhea can (in some cases) take the place of constipation: although this is quite normal, but if after 3-4 days the diarrhea does not pass, call your doctor.

It is believed that the main culprit of most of these symptoms, including mood swings and emotional breakdowns, is increased levels of estrogen and progesterone i.

If, during this period, you experience severe pain in the lower back, you have bleeding, blood clots and extreme nausea, it is advisable to contact your family doctor or gynecologist, as they could also be symptoms of a miscarriage.

Weight gain during the first trimester

Foetus. The increase in weight of the fetus in this first trimester is not remarkable: at the end of the first trimester, it is in fact as large as a peach.

Future mother. Although the speed of growth of the fetus is very subjective, the weight gain of the expectant mother at the end of the first three months should be about 1-2 kilos.

During the first three months of maternity, you can then continue to follow your regular diet (possibly healthy and balanced), and it will not be necessary for you to start eating for two!

When to announce that you have become pregnant

Once you have a pregnancy test with positive results, it is normal that you want to share the happy news with friends and acquaintances!

However, before making it public it is a good rule to wait until the end of the first quarter.

This is because, as the American College of Obstetricians and Gynecologists has clarified, about 10-25% of pregnancies end in miscarriage and about 75-80% of abortions occur within the first three months of pregnancy.

These percentages decrease dramatically after the 13th week: from 1% to 5%.

It is for this reason that it is preferable to be sure that the baby is well and keep the news “secret” for the first three months. Communicating an abortion is always a difficult and sad thing.

Prenatal checks and screening during this period

As soon as you find out you are pregnant, call your GP or midwife to schedule your first prenatal visit.

The midwife is the qualified health professional responsible for obstetric, gynecological and neonatal care.

It is a figure prepared to manage physiological pregnancy, from conception (to puerperium)[], and to recognize a possible pathology in order to be able (in this case only) to advise the expectant mother to consult the gynecologist.

The first check-up usually never takes place before the 8th week of pregnancy, unless there is a risk of complications, such as a previous history of miscarriages, or a family history of genetic diseases. This visit shall consist of:

  • checking for abnormalities in the growing embryo,
  • when calculating the date of termination of pregnancy,
  • in reviewing your medical history.

The screenings that are usually recommended for all women are those of HIV, syphilis, rubella, hepatitis B, as well as asymptomatic bacteriuria, chlamydia, toxoplasmosis.

Between the 19th and 21st week, an ultrasound examination is recommended, while the prenatal diagnosis of Down syndrome must be performed within 13 weeks: the woman must be informed of the abnormalities that may be found with the ultrasound, so that she can choose whether or not to keep the future baby.

Throughout the period of gestation, it is quite common practice to do monthly blood tests, and check blood pressure.

Some things to remember in the 1st trimester of pregnancy

During the 1st trimester of gestation, much of the development of your future child’s nervous system takes place.

Then, take the prenatal vitamin and folic acid supplements that are usually prescribed by your doctor.

During this time, avoid taking alcohol, caffeine and medications, as this is the period when there is a greater risk of developing neural tube closure defects (Dtn).

Neural tube closure defects (Dtn) are a group of congenital malformations caused by abnormalities of embryonic development that occur within 28 days of conception.

If you can, regularly practice the relaxation techniques you know best (yoga, tai-chi, meditation, etc.). Do regular physical exercises (after consulting your doctor) in order to reduce subsequent pregnancy disorders, and to better prepare your body for labor and birth.

Despite the fact that it is usually considered safe to fly during the first trimester, it is advisable to consult your gynaecologist or obstetrician before planning travel, especially in the case of high-risk pregnancy.

If you have recently become pregnant, it may also be useful to read our “List of necessary or useful things for the expectant mother in the 1st trimester of pregnancy”, you can find it here.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

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