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Pregnancy can completely transform a woman, in more ways than one. Hormonal fluctuations in the body can be held responsible for the physical and emotional changes experienced by the mother. A woman's body is remarkably transformed during pregnancy. These physical changes occur throughout the pregnancy - from conception to the time of delivery. The body of a woman goes into preparation mode right from the time of conceiving the child, and keeps adjusting accordingly.
Emotional changes, such as mood swings and even depression, might be overwhelming for a mother, especially so for a first-time mother. Physical changes also require a lot of adjustment on the part of the mother. While the most noticeable change in any woman who is carrying a child is the gradual weight gain, there is also a widening of the hips with the accumulation of fat at the hips, thighs and buttocks.
Another significant physical change in the woman happens in her breasts. Along with the growth in size, the shape and density of the breasts undergo a change as well.
While the most significant change in the breasts is the increase in size as the breasts equip themselves for feeding the newborn, there are many things going on with the breasts that bring about the change. This change is not overnight and happens gradually, spread over the entire nine months of the gestation period, with the change also continuing once the baby has been born.
During pregnancy, the breasts undergo changes at a rapid rate, changes that can be attributed to the heightened levels of certain hormones - progesterone, oestrogen as well as prolactin  - in the body. In addition to the hormone levels increasing, the body also prepares a buffer to accommodate the growing baby in the womb.
Breast Changes During Pregnancy
During pregnancy, a woman's body undergoes a lot of changes that can be referred to as hormonal, metabolic and immunologic.  While the changes are present both on the outside as well as the inside, the most prominent breast changes during pregnancy are the following:
1. Soreness, the most prominent change of them all, caused by increased levels of oestrogen and progesterone.
2. Heaviness, usually visible from the 6th week of pregnancy.
3. Increase in volume, studies reveal that while no two pregnancies are exactly the same in all respects, the volume of the breast increased by approximately 96 ml  on an average.
4. Transparency, the increased blood supply to the veins makes the veins seem darker, giving the impression of the breast turning transparent.
5. Nipples and areolas become larger  and change shape as well.
6. Nipples and areolas darken in colour.
7. Tingling sensation in the breasts.
8. Lumps and bumps, usually cysts or fibre tissues.
9. Leakage, colostrum starts oozing around week 16
11. Montgomery's tubercles, pimple-like structures around the nipple which secrete sebum to keep skin infections at bay.
12. A major breast change particularly seen towards the end of the gestation period, pain, is caused when the breasts become too full of milk for the baby.
13. Sagging of the breasts is usually seen towards the last stage of the pregnancy, with the sagging continues after the birth of the baby as well.
14. Stretch marks are caused as the breast greatly increases in size.
While the above-mentioned are the breast changes that appear at different stages of pregnancy, let us analyse the changes as they appear.
Also read: 5 Questions To Ask At Your First OB Appointment
Week By Week Analysis Of The Changes In The Breast
Studies have been conducted to ascertain if the increase in the size of the breasts along with the fluctuating asymmetry (FA) between the two breasts and other mammary changes are somehow related to the sex of the baby in the womb. After analysis of the studies conducted, it has been seen that women who report a comparatively larger increase in their breast size during the gestation period are more likely to be carrying a male foetus  .
Nevertheless, the changes that occur in the breast during pregnancy happen gradually and systematically.
Week 1 to week 4
In the womb, this is the egg's follicular and ovulatory phase. The very first change in the breasts is the growth of alveolar buds and milk ducts. This growth is at its peak in the second week when the egg is fertilized. The third week is significant as tenderness, generally considered to be one of the earliest signs of pregnancy, gets quite noticeable to the pregnant woman. Sensitivity around the nipples can be felt in the fourth week. This sensitivity is due to the increased blood supply to the breasts.
This period is when rapid reproduction of the milk-producing cells takes place, leading to a prickling or tingling sensation in the breasts.
Week 5 to week 8
A number of changes occur in the breasts between weeks 5 to 8 of the pregnancy. Hormones referred to as placental lactogens start interacting with the breasts. Massive changes happen in the cell structure of the breasts in order to equip them to handle the supply of milk later on. This is the period when almost all women report a feeling of fullness in their breasts accompanied with a marked heaviness as the milk ducts begin swelling.
The areolas or coloured area around each nipple, start turning noticeably darker in this period. This darkening is to enable the newborn to locate the breast with ease. Also, the nipples start sticking out. All these changes are reported in the fifth and sixth weeks. It is in the seventh week that the breast increases in weight to up to 650 grams on each side.
The eight week is significant for the appearance of Montgomery tubercles and 'marbling'. Montgomery tubercles, ranging from between a few to as many as 28 in number, are pimple-like enlarged pores that appear on the areolas, secreting an oily discharge to keep the nipples moisturized and safe from infections. Marbling is the growth of the veins below the surface of the breast.
Week 9 to week 12
The primary change in this period is that of the darkening and increasing of the size of the areola. This is also the time when a secondary areola develops and can be seen as a comparatively lighter-coloured tissue around the darker areola, often not visible among women with a light complexion. As by the 10th week, major growth in the breast is done, this is probably the best time for a woman to get a new bra. Nipple inversion is usually seen around the twelfth week of pregnancy. Though more commonly seen in first-time mothers, nipple inversion gets corrected on its own as the pregnancy progresses.
Week 13 to week 16
The 13th and 14th weeks are significant for the drastic increase in blood circulation. The areolas start looking more speckled than ever before. By the 16th week, breast tenderness generally goes away. This is also the period when a sticky fluid is discharged from the breasts. Referred to as colostrum, it is loaded with essential nutrients and resistance-building power for the newborn. At times, drops of blood might also be seen oozing from the nipple. While it is a common occurrence, a doctor can be consulted if the need is felt for an evaluation.
Week 16 to week 20
This is the time when the inevitable lumps and stretch marks make an appearance. As fat is accumulated in the breasts around the 18th week of pregnancy, lumps - fibroadenomas, galactoceles, cysts - appear on the breasts. These lumps are usually non-cancerous and nothing to fret over.
As the skin gets unduly stretched out due to the enlargement of the breasts, stretch marks become visible on the breasts, especially on the underside.
Week 21 to week 24
The breasts are at their biggest size during this period. As the fat accumulation causes breasts to sweat a lot, bras worn at this time should preferably be made of cotton. For the flow of blood to be unrestricted, underwire bras are not advisable to be worn at this period.
Week 25 to week 28
In this period, by the 26th week, the breasts are much fuller and even appear to be pendulous in some women. Though not true for every pregnant woman, in many women colostrum is also quite frequently secreted. By the 27th week, the breasts are ready for the production of milk. The hormone progesterone stalls the milk production until the time that the baby is born. The 28th week of pregnancy brings about a number of other changes, such as - blood circulation increases, area around the nipples darkens, milk ducts begin dilating and blood vessels below the skin become more visible to the naked eye.
Week 29 to week 32
The most prominent change in the breasts around the 30th week is the appearance of sweat rash. This happens due to the dilation of the blood vessels and the mucous membrane on account of the increase in the blood flow to the breasts. Sweat rash must not be ignored and treated accordingly to avoid the risk of further infection. The use of soap on the breasts should be avoided from the 32nd week of the pregnancy as the pimple-like bumps around the nipples are already producing enough creamy sebum to keep the skin well moisturised. The period between weeks 29 to 32 is also when stretch marks start becoming most visible.
Week 33 to week 36
Now, in almost all women, some amount of colostrum also starts secreting from the nipples. The nipples are more prominent than earlier. Week 36 is probably the best time to purchase a nursing bra, keeping in mind that the breasts will be fuller once the milk production starts and gradually get back to normal.
Week 37 to week 40
In the final phase of the pregnancy - that is, between weeks 37 to 40 - the colostrum changes colour from a yellowish liquid to a colourless and pale liquid. The breasts are fully matured to nurse the baby. Manipulation of the breasts by hand leads to the secretion of oxytocin, the hormone that induces contraction.
While the formation of lumps in the breasts is a common occurrence during pregnancy with a majority of the lumps being benign, there is still the chance of such lumps being cancerous. Though rare (around 1 in 3,000)  , there are chances of a pregnant woman developing pregnancy-associated breast cancer.
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-  Bayer, C. M., Bani, M. R., Schneider, M., Dammer, U., Raabe, E., Haeberle, L., ... & Schulz-Wendtland, R. (2014). Assessment of breast volume changes during human pregnancy using a three-dimensional surface assessment technique in the prospective CGATE study. European Journal of Cancer Prevention, 23(3), 151-157.
-  Thanaboonyawat, I., Chanprapaph, P., Lattalapkul, J., & Rongluen, S. (2013). Pilot study of normal development of nipples during pregnancy. Journal of Human Lactation, 29(4), 480-483.
-  Żelaźniewicz, A., & Pawłowski, B. (2015). Breast size and asymmetry during pregnancy in dependence of a fetus's sex. American Journal of Human Biology, 27(5), 690-696.
-  Beyer, I., Mutschler, N., Blum, K. S., & Mohrmann, S. (2015). Breast Lesions during Pregnancy - a Diagnostic Challenge: Case Report. Breast care (Basel, Switzerland), 10(3), 207-210.