If you’re trying to conceive, you’ll constantly be on the lookout for early pregnancy symptoms — and an implantation bleeding, which sometimes occurs when the newly fertilized egg nestles into the uterine lining, is one of the earliest possible pregnancy signs.
How do you tell the difference between an implantation bleeding and a period, though?
You could suspect it is an implantation bleeding if it occurs a bit earlier than your expected period and if the bleeding is scanty, spotty, pinkish and not red and heavy like a period. If your bleeding does not follow the normal pattern of a period, it is probably an implantation bleeding and not a period.
What Does An Implantation Bleeding Look Like?
There is often the feeling that it is a period with light cramps and bloating, but the bleeding is shorter, lighter and simply not normal. If a woman is usually regular, and now all of a sudden develops this type of early spotting after unprotected intercourse, pregnancy is a possibility. Each woman should understand that an implantation bleeding occurs during the implantation of the egg cell. It occurs towards the end of the implantation process. 
Trophoblast is a highly specialized tissue, which develops from the fertilized egg and surrounds the egg. It attaches the egg to the endometrium. As it is continuously growing, it invades the endometrium, and it eats its way into the endometrium. It pulls the egg into the endometrium. The trophoblast also invades the mother's blood vessels and diverts her blood to cavities inside the trophoblast.
These cavities are then filled by maternal blood becoming "blood lakes", and most of these lakes are connected. The trophoblast on the outer surface of the egg are thinner and slower growing but also contain cavities that are connected to other deeper cavities. Some of these outer cavities communicate or open into the uterine cavity.
Blood that leaks from these cavities cause an implantation bleeding, and it occurs shortly before the egg is completely implanted and completely covered with endometrium. 
Implantation bleeding has no adverse effects on a pregnancy, although some experts doubt the existence of implantation bleeding. If you search for implantation bleeding you will come across sites that doubt if it ever occurs, but the fact is that some women, about 1%-2%, have a bleeding about four weeks after the last menstrual period with a pregnancy duration four weeks longer than expected. 
When Does Implantation Bleeding Usually Occur?
It can happen at the time the fertilized egg implants in the uterus, on average between six to twelve days past ovulation (average 9.1 days).
Home Pregnancy Tests
A home pregnancy test detects the hormone Human Chorionic Gonadotropin or hCG in a woman’s urine. This hormone is a hormone secreted by the developing placenta shortly after a fertilized egg has been implanted in the uterine lining, so if a woman is pregnant, the amount of Human Chorionic Gonadotropin in her system should be around 25 mIU at 10 dpo.  (Dpo means days past ovulation.)
It is also 50 mIU at 12 dpo, and 100 mIU at around two weeks dpo. Because of their high sensitivity factor in detecting human hCG, pregnancy tests can confirm pregnancy as early as 6-8 days past ovulation. To help lower the chances of a false negative, the best time to do a home pregnancy test is at least 9-10 days past ovulation.
What Else Can Cause Vaginal Spotting?
Vaginal bleeding is considered abnormal if it occurs:
- before or after you are expecting your regular menstrual period, or when your menstrual flow is considerably lighter or heavier than what is normal for you.
- at a time in life when this should not be the case, for example when you’re pregnant or after your menopause or in young girls, usually before the age of 9.
Many women experience abnormal vaginal bleeding or spotting between their regular periods, and this is not always a cause for concern.
If you are pregnant:
- You may have very scant implantation bleeding, possibly around 11 or 12 days after fertilization. It is close to the time you might notice a missed period. It may be caused by the fertilized egg burrowing into the wall of your uterus, a process that starts just six days after fertilization, but no one knows for sure. The bleeding is very light, lasting only a day or two, and only a minority of pregnant women experience this kind of spotting aka implantation bleeding.
- A miscarriage or an ectopic pregnancy often causes vaginal spotting, especially if it’s heavy and after 12 weeks of pregnancy. Spotting can be an early sign of miscarriage or an ectopic pregnancy, especially if accompanied by abdominal pain or cramping. About a quarter of pregnant women have some spotting or bleeding in early pregnancy, and about half of these women miscarry, but if you have an ultrasound that shows a heartbeat between 7 and 11 weeks, your chances of continuing the pregnancy are greater than 90 percent. 
- Placental problems or premature labor also cause spotting in some women. In the second or third trimester, bleeding or spotting can be a sign of a serious condition such as placenta previa, placental abruption, a late miscarriage, or premature labor. A mucus discharge that is tinged with blood after 37 weeks is most likely just a sign that the mucus plug has dislodged and the cervix is beginning to soften or dilate in preparation for normal labor. 
- It is also important to know if your blood is Rh-negative, you will need a shot of Rh immune globulin whenever you have vaginal spotting or bleeding. It is necessary unless you know for sure that the baby’s father’s blood is also Rh-negative.
During pregnancy there is an increase in the blood supply to your cervix and greater blood flow to the area. This is why you might bleed unexpectedly and oftentimes vaginal bleeding shouldn’t be a reason for concern. For example, you might be spotting after having a simple Pap smear or internal gynaecological exam or even during or after sexual intercourse. 
If you are NOT pregnant:
- Some women lightly bleed during ovulation, while women with polycystic ovary syndrome (PCOS) might experience bleeding because imbalanced hormones interfere with their ovulation
- An intrauterine device (IUD) or birth control pills sometimes cause abnormal vaginal bleeding, especially if you have just recently started using them.
- Spotting can also be caused by conditions unrelated to pregnancy, for example, because of vaginal infection, such as a yeast infection or bacterial vaginosis.
- In some cases, sexually transmitted infections, such as trichomoniasis, gonorrhea, chlamydia, or herpes can cause your cervix to become irritated or inflamed.
- Pelvic inflammatory disease (PID) and even an inflamed cervix are particularly susceptible to spotting after sex or after a Pap smear, and you may also spot or bleed after sex or a Pap smear if you have a cervical polyp. In general, an infection of the pelvic organs is very susceptible to abnormal abdominal bleeding, especially after an internal exam, intercourse or even douching, which should never be a part of woman’s hygiene.
- Abnormal vaginal bleeding can be a sign of cancer of the pelvic organs.
- Sometimes even stress and excessive exercise can cause vaginal spotting. Structural problems of the pelvic organs, such as uterine prolapse, polyps or fibroids, and even diseases such as hyperthyroidism or diabetes can cause abnormal vaginal bleeding.
Most likely you will not notice any symptoms until about the time you have missed a period or a week or two later. If you are not keeping track of your menstrual cycle or if it varies widely from one month to the next, you may not be sure when to expect your next period. However, if you start to experience some of the symptoms below and you have not had a period for a while, you may very well be pregnant. You could take a home pregnancy test to find out for sure.
The most common pregnancy signs are :
Tender and swollen breasts
One of the early signs of pregnancy are sensitive, sore breasts caused by increasing levels of hormones during pregnancy. The soreness may feel like an exaggerated version of how your breasts feel before your period, and your discomfort should diminish significantly after the first trimester, as your body adjusts to the hormonal changes.
If you feel tired all of a sudden or even exhausted it could also be a pregnancy sign. No one knows for sure what causes early pregnancy fatigue, but it could possibly be that rapidly increasing levels of the hormone progesterone are contributing to a woman’s sleepiness. You should start to feel more energetic once you hit your second trimester. However, fatigue usually returns late in pregnancy when you are carrying around a lot more weight and some of the common discomforts of pregnancy make it more difficult to get good night’s sleep.
Some women have a small amount of vaginal bleeding called implantation bleeding, around 11 or 12 days after conception, close to the time you might notice a missed period. The bleeding may be caused by the fertilized egg burrowing into the blood-rich lining of the uterus. This process starts just six days after fertilization, but as I already said, no one knows that for sure. The bleeding is very light, appearing as red spotting or pink or reddish-brown staining, and lasts only a day or two. You should let your practitioner know if you notice any bleeding or spotting, particularly if it is accompanied by pain since this can be a sign of an ectopic pregnancy.
Nausea or vomiting
If you are like most women, morning sickness will not hit you until about a month after conception. A lucky few women escape it altogether. However, some women do start to feel queasy a bit earlier and not just in the morning; pregnancy-related nausea and vomiting can be a problem morning, noon, or night. About half of women with nausea feel complete relief by the beginning of the second trimester while for most others it takes another month or so for the queasiness to ease up.
Increased sensitivity to odors
If you are newly pregnant, it is not uncommon to feel repelled by the smell of a bologna sandwich or cup of coffee and for certain aromas to trigger your gag reflex, which could be a side effect of rapidly increasing amounts of estrogen in your system. You may also find that certain foods you used to enjoy are suddenly completely repulsive.
Hormonal changes in early pregnancy may leave you feeling bloated, similar to the feeling some women have just before their period arrives, which is why your clothes may feel snugger than usual at the waistline, even early on when your uterus is still quite small.
Shortly after you become pregnant, you may find yourself hurrying to the bathroom all the time, mostly because during pregnancy the amount of blood and other fluids in your body increases, which leads to extra fluid being processed by your kidneys and ending up in your bladder.
A missed period and basal body temperature stay high are signs for pregnancy you probably already know to recognize.