What is implantation? Symptoms, when it happens & more

What is implantation?

Implantation is when a fertilized egg embeds itself in the uterine lining, officially marking the beginning of pregnancy [1, 2]. Let’s look at the full process from ovulation to fertilization to implantation. 

When you ovulate, a mature egg cell is released from one of your ovaries. If the egg cell meets a sperm cell, it can be fertilized [3]. Once fertilization is complete, the fertilized egg — now called a zygote — travels down the fallopian tube to the uterus [4]. During its journey, the zygote rapidly divides into a multicellular organism called a blastocyst that implants into the uterine lining. Part of the blastocyst will eventually become the placenta, and the other part the embryo [1]. Implantation allows your body to support the growing embryo by providing nutrients and chemical signals through the uterine lining [5].

When does implantation occur?

Implantation happens very early in pregnancy, from 8 to 10 days after ovulation [6]. So, for example, if you ovulate on day 14 of your cycle, implantation would happen around day 22 to 24. However, cycle length and ovulation vary from person to person, and even from cycle to cycle. 

Traditionally, the medical community has estimated that most females have a 28-day cycle and ovulate around day 14. But a Natural Cycles study of over 600,000 cycles found that menstrual cycles vary much more than originally thought. The study found the average cycle length was 29 days, but about 90% of cycles ranged from 21 to 35 days; and ovulation happened, on average, on cycle day 17, but again varied widely, from day 10 to day 30, depending on the individual [7]. 

All this to say that implantation timing is unique to you and your cycle. Tracking ovulation can be difficult, but Natural Cycles makes it simple. The NC° app uses a specialized algorithm that analyzes your unique cycle data, and your body temperature to predict ovulation. Using the Calendar View in the NC° app, you can clearly see when you are likely to ovulate, then work out when, if fertilization occurs, implantation might happen. This makes it easier to match any small symptoms you’ve experienced with whether they may be linked to implantation. 

“I got a lot of my information on the Natural Cycles app. Through tracking my cycles for a year [on NC° Birth Control], I learned so much about my body during that time. It helped me be able to notice the signs of my most fertile days, especially when I switched to planning pregnancy.” - Hailey, NC° user

Implantation and IVF

If you are conceiving using in-vitro fertilization (IVF), implantation can look a little different. Embryos are usually transferred into the uterus two to six days after fertilization [8]. Implantation typically happens a few days later, but the timing depends on the age of the embryo [9]. Your medical provider will guide you through everything you need to know, and it's important to follow your clinic’s advice about when to test as testing too early could lead to a false positive [10, 11].

Implantation symptoms

Most people won’t notice when implantation happens, and won’t experience any clear implantation symptoms either. But for some, subtle signs might hint at what is happening in your body, such as:

• Cramps: Implantation cramps are typically described as similar to period cramps, but milder, with a prickly, tingly, or pulling sensation. Unfortunately, most reports are anecdotal, and more research is needed to confirm that this phenomenon is definitely related to implantation. 
• Bleeding: Another commonly reported symptom is implantation bleeding. Up to 25% of pregnant women experience light spotting in their first trimester, some of which might be linked to implantation [12]. However, there are several causes of bleeding in early pregnancy, and again, there is currently a lack of research in this area. 
• Body temperature: Some people also experience a one-day dip in basal body temperature (BBT) around the time of implantation, before it rises back to the usual luteal-phase levels. This is often called an implantation dip. A slight drop around this time may relate to the secondary estrogen surge in the luteal phase, as estrogen is known to lower body temperature [13, 14, 15]. We know BBT changes in pregnancy — typically hormones cause it to stay high after the end of the luteal phase (instead of lowering when your period starts). However, no research currently supports the idea that implantation causes a dip in BBT, and the secondary estrogen surge typically happens in all menstrual cycles, whether implantation occurs or not. 

Everyone experiences early pregnancy and implantation differently. Though your friend or family member might have experienced implantation symptoms, it's completely normal not to notice anything, too. If you have any concerns about implantation, fertility, or your menstrual cycle, speak to your healthcare provider. 

Implantation bleeding vs period

You might be wondering how to tell the difference between implantation bleeding and your period, and the good news is that for most people, there are clear differences.

The first is timing. Implantation typically happens 8 to 10 days after ovulation, whereas your period usually starts slightly later, 10 to 16 days after ovulation [16]. For some, especially those who track their cycle, this might help determine which you’re experiencing. But because these timing windows overlap, people with irregular cycles or lighter periods might find it harder to tell the difference between their period and implantation bleeding.

“If you’re trying to get pregnant, understanding what happens during the parts of the cycle, when ovulation is happening, when intercourse should happen, will optimize your chances of conceiving” - Dr. Karen Tang, Board-Certified OBGYN & Natural Cycles Medical Advisor

The second characteristic to consider is the bleed itself. Your period is typically heavier and lasts between two and seven days [16]. Implantation bleeding is usually a lighter, pink or brown spotting or discharge.

Whilst light bleeding in early pregnancy is common and usually not a cause for concern, if you’ve had a positive pregnancy test and experienced any unexplained bleeding or pain, speak to your healthcare provider as soon as possible. Sometimes, heavy bleeding can be a sign of a miscarriage, or in rare cases, a serious condition, like ectopic pregnancy [17, 18]. 

When to take a pregnancy test 

If implantation is successful, pregnancy officially begins [2]. The developing embryo will begin producing hCG hormone from implantation, but levels are still too low for pregnancy tests to pick up. 

The best time to take a pregnancy test is after your missed period, or if you have unpredictable cycles, three weeks after having unprotected sex [19, 20]. You can test earlier, and some tests are specifically designed for earlier detection. But you are more likely to have a false negative if your hCG levels are still too low. As we mentioned above, if you are using IVF, follow the advice from your clinic about when to test, as you could have a false positive if you test too early. If you have a positive pregnancy test result, make an appointment with your doctor so they can confirm and arrange the necessary early pregnancy checks and tests. 

“It is exciting and nerve-racking to take a pregnancy test. It is a moment of panic and happiness all at the same time. There are so many things that can go wrong but also a lot of positive things.” - Shea, NC° user

Other early pregnancy symptoms

Whilst you wait to take a pregnancy test, you might start to notice some symptoms as your hormones change and your body starts nourishing your growing baby, especially if you are already in tune with your usual menstrual cycle symptoms. 

Below are some of the most common early pregnancy symptoms. But remember, everyone’s pregnancy is different, and not everyone will experience these. Many of these symptoms are also very similar to premenstrual syndrome (PMS), which would typically happen around the same time in your cycle. These symptoms include:

• Nausea: This can be mild or severe, and may or may not lead to vomiting. Although often called morning sickness, it can happen at any time of day!

• Fatigue: Extreme tiredness whilst doing your usual daily activities is common in the first few weeks of pregnancy.

• Breast pain: Your breasts may become larger or feel tender, similar to the breast pain you might feel before your period.

• More vaginal discharge: It is common to notice more vaginal discharge than usual when you are pregnant.

• Changing senses: You might notice a metallic taste in your mouth, become more sensitive to certain smells, or notice a change in your food preferences or cravings.

[21]

“Once a pregnancy implants, your progesterone levels will increase, leading to many of the early pregnancy symptoms. These symptoms can include nausea, lack of appetite, sensitivity to smell, food aversions, enlarged and/or tender breasts, bloating, and fatigue. Every person and every pregnancy is different.” - Dr. Natalie Crawford, Natural Cycles Medical Advisor

A note on the two-week wait

The time from ovulation to confirming a pregnancy is often called the “two-week wait”. There is no right or wrong way to feel during this time. Some people find it exciting, while others find it very emotional. The important thing is to look after your health and wellbeing, and it can be helpful not to overthink small symptoms in the run-up to taking a pregnancy test. 

When to see a doctor

Always speak to your healthcare provider, midwife, or doctor if you have any worries about unexpected bleeding, irregular periods, implantation symptoms, or fertility, especially if: 

• You have been trying to get pregnant for over 12 months (or six months if you are over the age of 35)
• You are trying to get pregnant and have a reproductive or long-term health condition, such as epilepsy, PMOS (formerly PCOS), endometriosis, or a sexually transmitted infection (STI)
• You have tested positive for pregnancy and experience unexplained or heavy bleeding
• Your period is very heavy, soaking through one or more pads or tampons every hour, or lasting for longer than seven days
• Your period is very painful, or you experience severe PMS
• You experience bleeding or pain during sex
• You regularly experience bleeding or spotting between periods
• Your menstrual cycle is longer than 35 days or shorter than 21 days
• Your menstrual cycle length varies by more than seven to nine days
• You haven’t had a period for three to six months, known as amenorrhea
• You experience bleeding after menopause (when you haven’t had a period for a year or more)

[17, 22, 23]

Feel empowered in your fertility with Natural Cycles

Natural Cycles is here to help you learn more about your menstrual cycle and fertility. Using skin temperature readings from your chosen wearable device and your unique cycle characteristics, our one-of-a-kind algorithm will predict ovulation, your fertile window, and your period each cycle. The NC° app is FDA-cleared to help you conceive. You’ll know when you are at your most fertile each cycle, can log when you’ve had sex, and make notes about any symptoms you experience, like implantation symptoms or PMS. You can even share your fertility status with your partner, and, on average, couples who use NC° Plan Pregnancy conceive within three cycles [24]. Once you’re pregnant, you can track your baby’s growth and development with NC° Follow Pregnancy, and support your recovery after birth with NC° Postpartum.