It has to do with the bromeline in the core, which can help with implantation. For the life of me I can't find the link where I saw that but I did copy/paste the language into another thread that I'll post here:
"Using Pineapple core to Assist Implantation: Pineapple contains bromelain. Bromelain is a proteolytic enzyme that breaks up proteins that inhibit embryo implantation. Consuming a whole pineapple (focusing on the core as it has the highest concentration of Bromelain) during a fertility cycle can be beneficial.
For IVF [in vitro fertilization] cycle: one pineapple core, divided into 5 portions - consume one portion each day, over five days, beginning on the day of your embryo transfer.
IUI [intra-uterine insemination] cycle: one pineapple core, divided into 5 portions - consume one portion each day, over five days, beginning on the day of your IUI.
Timed intercourse cycle: one pineapple core , divided into 5 portions - consume one portion each day, over five days, beginning on the day after ovulation.
Note: Be careful not to start consuming pineapple core too early in the cycle. Beginning to consume pineapple core BEFORE the recommended days above can actually affect your vaginal and cervical mucus PH, making it more acidic.
Here is a website to better clairify:http://howtocutapineapple.com/
Do NOT eat the meat of the pineapple- You need to AVOID Pineapple Juice. Do NOT take with Baby Aspirin as these are BOTH blood thinners! Pineapple juice is not recommended for use in TTC and/or pregnancy. In large doses, it can cause uterine contractions and bring on spontaneous abortions (miscarriage).
Side Effects: Large doses may cause uterine contractions, miscarriage, vomiting, diarrhea, skin rash, very heavy menstrual periods. Unripe pineapple is poisonous, causing excessive diarrhea.
Bromelain Tablets/Capsules- Bromelain is used for many things, some believe that this can be used to aide in implantation of an embryo. When taking this, these are stronger than a pineapple core would be. A pineapple core is 50mg of bromelain. Any bromelain tablets are 300-500mg, some do have 80mg's though. . Do not take if allergic to pineapple.
Bromelain is a mixture of protein-digesting (proteolytic) enzymes found in pineapples (Ananas comosus ). Pineapple has been used for centuries in Central and South America to treat indigestion and reduce inflammation. Bromelain, which is derived from the stem and juice of the pineapple, was first isolated from the pineapple plant in the late 1800s. It is approved by the German Commission E to treat swelling and inflammation following surgery, particularly sinus surgery.
Bromelain can be useful in treating a wide range of conditions, but it is particularly effective in reducing inflammation associated with infection and injuries.
Website for more information with Bromelain:http://www.umm.edu/altmed/articles/bromelain-000289.htm