Many varied abbreviations are used, some common all over the 'Net, such as LOL (Laugh Out Loud) some are more specific to endo or infertility groups.
AFAIK: As Far As I Know
AI: Artificial Insemination
BBT: Basal Body Temperature
BCP/s: Birth Control Pill/s (also referred to as Ovulation Control Pills)
BTW: By The Way
CBPC/s: Continuous BCP/s
CD: Cycle Day
CF: Cervical Fluid
CM: Cervical Mucous
CVS: Chorionic Villae Sampling
D&C: Dilation & Curettage
D&E: Dilation & Evacuation
DE: Donor Eggs
DH: Dear Husband
DI: Donor Insemination
DP: Depo Provera
Dx: Diagnosis
E2: Estradiol
ENDO: Endometriosis
EPT: Early Pregnancy Test
ET: Embryo Transfer
FAQ: Frequently asked Questions
FET: Frozen Embryo Transfer
FSH: Follicle Stimulating Hormone
FWIW: For What It's Worth
GIFT: Gamete Intra-fallopian Transfer
GnRH: Gonadotropin Releasing Hormone
GP: General Practitioner
GYN: Gynaecologist
HCG: Human Chorionic Gonadotropin
HCP: Health Care Practitioner
HPT: Home Pregnancy Test
HRT: Hormone Replacement Therapy
HSG: Hysterosalpingogram
HTH: Hope That Helps
ICI: Intra-cervical Insemination
ICSI: Intra-cytoplasmic Sperm Injection
IF: Infertility
IIRC: If I Remember Correctly
IM: Intra-muscular
IMO: In My Opinion
INCIID: International Council on Infertility Information Dissemination
IUI: Intra-uterine Insemination
IVF: In Vitro Fertilization
LAP: Laparoscopy
LH: Luteinizing Hormone
M/C: Miscarriage
MIL: Mother in Law
MRI: Magnetic Resonance Imagery
OB: Obstetrician
OB/GYN: Obstetrician/Gynaecologist
OPK: Ovulation Predictor Kit
OTC: Over The Counter
PCOS: Polycystic Ovarian Syndrome (also PCO, PCOD)
PCP: Primary Care Physician
PCT: Post Coital Test
PG: Pregnant
PI: Primary Infertility
PID: Pelvic Inflammatory Disease
PMS: Pre-menstrual Syndrome
POF: Premature Ovarian Failure
PTSD: Post-traumatic Stress Disorder
RE: Reproductive Endocrinologist
ROFL/MBO: Rolling On the Floor Laughing/My Butt Off
RSA: Recurrent Spontaneous Abortion
Rx: Prescription
SA: Semen Analysis
SI: Secondary Infertility
SLE: Systemic Lupus Erythematosus
SO: Significant Other
STD: Sexually Transmitted Disease
TET: Tubal Embryo Transfer
TIA: Thanks In Advance
TSH: Thyroid Stimulating Hormone
TUFT: Trans-uterine Fallopian Transfer
Tx: Treatment
U/S: Ultrasound
UTI: Urinary Tract Infection
WBC: White Blood Cells
YMMV: Your Methods May Vary
ZIFT: Zygote Intra-fallopian Transfer