Pregnancy is a state of conception in which maternal body undergoes various physiological, anatomical and biological changes to adapt to the growing needs of the baby. These changes are present in the whole body and if one is not well versed with the physiology of pregnancy he/she might interpret these changes as pathology i.e. some kind of disease. Also, knowing about these changes help us diagnose the pregnancy and if there is a risk associated with it.
Now, these changes come and go as per the stage of pregnancy which is determined by the trimester which you are in. To know about these trimesters we need to know a few things:
Duration Of Pregnancy
Traditionally, the duration of pregnancy is considered of about 280 days or 40 weeks or 9 months + 7 days. Now, what is this duration? This duration is calculated from the first day of the last menstrual period to the delivery of baby. In most cases, last day of this duration is considered expected date of delivery i.e. due date, which can move one week up or down in a healthy pregnancy.
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Period Of Gestation
In layman term, it is the age of your growing baby. It is a little different from duration of pregnancy. While duration of pregnancy tells about the due date, POG (period of gestation) tells about the fetal age. POG is not fixed and increases after every single day of pregnancy. It is calculated from the first day of last menstrual period to today – 14 days. Why 14 days subtraction? Well, in a normal menstrual period we consider that fertilization occurs after a period of 14 days following the last menstrual period.
Now that we know about duration of pregnancy, let’s discuss about the different trimesters and changes we expect in them. We will be learning about the changes in maternal body not in the fetal body.
Stages Of Pregnancy
We need to know a few things about a stage of pregnancy and that is what we will be discussing in each stage. Stages being classified as first, second and third trimester. Few things we will be talking about are:
- Duration of each trimester
- Sign and symptoms in each trimester
- A little about fetal development
First Trimester Of Pregnancy
Duration of first trimester
First trimester starts from the first day of last menstrual period and lasts up to the 12 weeks of pregnancy. Practically 3 months, but it will be foolish of us to divide 40 weeks in 3 months each and call them a trimester because then 7 days go unaccounted. So, from now onwards we will be talking in terms of weeks.
Symptoms presenting in first trimester
Amenorrhea – Amenorrhea is the medical term for absence of menstrual period in the end of month. This is the first symptom presenting in pregnancy and it remains throughout the pregnancy. Why so?
Menstrual cycles are there to prepare uterine endometrium for the conceptus i.e. the fetus. Hormonal changes occurring in a female body during a menstrual cycle all lead to making endometrium more muscular and ready if she conceives the baby, but what happens when baby is not conceived. In that case endometrial shedding results i.e. the period we know of. In pregnancy, baby is conceived so there is no need of endometrial shedding and hence no periods.
Although some amount of scanty bleeding can be observed due to other reasons but that is not menstrual bleeding. It is called placental sign, and is due to ovum implantation. It may coincide with the expected menstrual date but the bleeding is very scanty.
Morning sickness – Morning sickness is early morning nausea and vomiting seen in pregnancy rarely lasting beyond first trimester. Though cause is uncertain, high HCG levels seen in the first trimester are usually associated with morning sickness.
Increased frequency of urination – Frequent bathroom breaks is the most common complaint in pregnant females but it not pathological. Due to certain physiological changes polyuria develops in pregnancy. These changes are
- Changes in maternal osmoregulation causing increased desire to drink water and thereby increased urination.
- Enlarged uterus compressing the bladder, along with congestion in bladder mucosa causing frequent bathroom breaks.
Breast discomfort – Due to maternal hormonal changes, chiefly oestrogen and progesterone, breast enlargement occurs in pregnancy. They are tender and more sensitive which causes generalized breast discomfort. Breast changes are also associated with changes in nipple. Nipple and areola become more pigmented, Montgomery’s tubercle may be present. Colostrum expression can be observed as early as 12 weeks.
Fatigue – Fatigue is generalized tiredness, exhaustion. This is due to apparent changes your body is going through. You need extra energy, extra strength for this change and your body is preparing you for this but it takes some time. Meanwhile, hormones are racking up your system making fatigue more prominent.
Apart from these symptoms, there is heartburn, mood swings, cravings for different food items etc., which may be seen in some females. There are also certain vaginal and cervical signs which should better be elicited by doctors. Unusually high HCG levels help diagnose the pregnancy by dipstick method in the first trimester.
Fetal development in first trimester
Fetal development is so vast and huge that it can never be completed in one paragraph. Here we will talk about what structure will be presented in a 12 weeks fetus and their functionality. In a growing fetus heart is the first organ to be formed, by the end of 4 weeks fetus has a heart of its own and is functional. By the end of 12 week an audible heartbeat can be heard via ultrasound.
Apart from this fetus genitalia can be differentiated by the end of 12 weeks. Facial features like external ear, eyelids are easy to make out though fetus is only about 1-1.5 inches. Gut starts developing, pancreatic buds, tooth buds are present. Limbs are well-formed and liver starts forming RBCs.
Second Trimester Of Pregnancy
Duration of second trimester
2nd trimester starts by the end of 12th week and ends till 27th week. Babies born before 27 weeks have a very low survival rate and usually fail to thrive. Apparent reason is failure of lung development and various other organs completely. Lung does not develop fully by the end of 34 weeks.
Symptoms presenting in second trimester
Symptoms like nausea, vomiting, fatigue, increased urination frequency etc. disappear by the 2nd trimester. Amenorrhea stays but you get used of it. Certain new symptoms develop in your body but still it is a relatively easier time for a mother.
Quickening – Quickening is a term for fetal movement perception by mother. Around 18 weeks baby starts kicking inside the womb and mother appreciates them, rather anyone can feel them if he/she keeps his hand over the tummy. It is a good measure to get an estimate of delivery and about fetal development.
Breast changes – Previously observed breast changes becomes more prominent. Further breast enlargement occurs, veins are quite prominent on breasts. Montgomery tubercle and nipple-areola pigmentation is further enhanced.
Striae and linea nigra – Linea nigra is brownish streak extending from pubis to umbilicus seen in pregnant females around 2nd trimester. It is observed due to MSH(melanocyte stimulating hormone) produced by placenta, more observed in dark complexion people. MSH is also responsible for Chloasma – dark pigmentation over forehead and cheeks presenting around 24 weeks.
Striae are pink and white stretch mark presenting in lower abdomen due to stretching of abdominal wall by enlarging uterus, enlarging uterus causes tearing in dermis of abdominal skin leading to striae.
Braxton-hicks contraction – These uterine contraction start from early pregnancy and can be felt 2nd trimester onward. Although they are quite different from true labour contraction yet an inexperienced individual should never try to rule out so. The contractions irregular, infrequent and relatively painless.
Fetal parts per abdo – In 2nd trimester one can easily appreciate fetal limbs and curved knobby back after abdominal wall palpation. With help of a stethoscope, fetal heartbeat can also be heard. Fetal heart beats faster than adult heart about 120 – 160 beats per minute, so try to appreciate that.
Fetal development in second trimester
In 2nd trimester a lot happens. Fetus is quite active, brain functional and more developed. Liver and pancreas who were immature in 1st trimester, starts secreting enzymes. Eye development is complete, fetus can also open his eyelids by now. External genitalia are completely formed and ultrasonic prediction of sex is quite accurate. Immature lungs start exchanging gases, though they won’t survive in external environment, yet they start doing their job.
Ultrasound is advised in 2nd trimester to look for any fetal organ anomaly, so you should definitely not avoid that.
Third Trimester Of Pregnancy
Duration of third trimester
Duration of third trimester may vary depending on the delivery of baby. In general, it considered from 28th week to 40th week of pregnancy, but in postterm delivery it may very well go beyond 40 weeks. Similarly, in preterm deliveries it can be lesser than 37 weeks.
Any delivery before 37 weeks is considered preterm delivery and any delivery beyond 42 weeks of pregnancy is considered post term delivery. Both of these conditions have risk of their own, preterm being more riskier.
Symptoms presenting in third trimester
In last trimester of pregnancy, increased urinary frequency, heartburn reappears. Of course, amenorrhea persists. Uterine enlargement is so much that it starts causing symptoms of its own like shortness of breath and rapid heartbeat. Fetal movement becomes frequent and other symptoms seen in 2nd trimester becomes more prominent.
Lower limb swelling – This is not a physiological symptom but a pathological one, but as this complaint is so much common in pregnant females it is worth mentioning. It might be nothing but it can be a sign of pre – eclampsia in which hypertension and proteinuria ensues. It can further get complicated if seizure presents, such cases usually undergo C sections to prevent mortality.
Lightening in pregnancy
As uterus descents down from abdominal cavity around 38 weeks and becomes a pelvic organ. Pregnant females feel a sense of relief as pressure inside the abdominal cavity is decreased. This is a physiological change and you should enjoy this relief till it lasts.
Fetal development in third trimester
Fetal development is crucial in third trimester. Although, most of the body organs develop in 2nd trimester, they mature in 3rd trimester. Lungs get matured by 34 weeks and any delivery after 34 weeks has significantly higher survival rate compared to that before 34 weeks. Fetus start gaining weight, storing minerals and micronutrients. Body fat increases significantly. Bones, muscle development is complete. Brain starts functioning fully.
By the 39th week baby is fully developed, weighing about 2.5 – 3 kg and with length of 48-53 cm. Again these values are for a healthy full term baby. A baby delivering after 42 weeks will be a larger baby, while a baby delivering before 37 weeks will be low weight baby.
This is the brief version of all you need to know about the various stages of pregnancy – duration, symptoms, development everything. However, if you find yourself distressed because of any symptoms above mentioned or not mentioned, I would advise you to go to your obstetrician and act as per his advice.
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