Currently active bills include:

• Montana's SB 406 — passed the Senate by 26-24 on Feb 26, still must pass in the House
• North Dakota's HB 1572 — passed the House by 51-41 on Feb 17, still must pass in the Senate
• (see below for previous unsuccessful efforts)

Reproductive side effects

• No exceptions for rape or incest. This couldn't be argued over, it would be decided already.
• Exceptions to preserve the mother's life would be long and drawn-out, since the court would have to decide "which life is more valuable than the other". One common example of this is ectopic (tubal) pregnancies, a medical emergency that can kill the mother, it occurs in ~1% of pregnancies.
  HR 1572 tries to head off endless debate by explicitly clarifying that the mother's life is more important than the baby's. "If a pregnant woman's health is in danger during a pregnancy, the physician may not be held criminally responsible for unintentionally causing the death of the preborn human being from legitimate treatment administered to the pregnant woman."
  
  SB 406 doesn't weigh in on this issue, thereby leaving it up to the courts to hash out.
• Birth control that prevents implanting would be outlawed.
  • Unfortunately, the issue is sometimes complicated. Many on the far right, along with a small number of scientists, believe that a wide range of contraceptives work both to prevent fertilization and to prevent implantation. Most scientists think it's clear that even if a drug were able to act in both phases of pregnancy, most of them are successful in preventing fertilization in the vast majority of cases. However, opponents say that until it's proven that they don't act as implantation-preventers, that they should be classified as abortificants. So far, this has largely been an argument inside conservative circles only; this law would require judges to weigh in on the issue for the first time.
• Criminal negligence would extend to cover things the mother ingested during pregnancy.
  • In particular, there could be a "chilling effect" where doctors would be less willing to prescribe medicine until after pregnancy if there was any chance that the medicine could be tied to later complications.
    (yet another reason why HR 1572 states that the mother's life is more important than the baby's)
• ~65% of zygotes fail before a doctor can ever notice them. Hospitals could be compelled to do everything possible to 1) detect these previously undetected fertilizations, and 2) ensure that as many as possible implant successfully. If hospitals fail to act, it could be equivalent to allowing poor people die outside the emergency room because they couldn't pay.
  It's speculation on my part, but I believe conservatives wouldn't actually require hospitals to do this. 1) It's extremely costly, and 2) it doesn't fit in with the far-right's "childbearing must go back to occurring the way god intended it!" mantra, not in the way that banning birth control does. (the "snowflake baby" movement gets the closest of anyone)
  If conservatives in fact don't force hospitals to do this, then it may be a public admission that this was all a means-to-an-end (sound familiar?), and that they don't actually directly care about the supposed principle

  It's even more inconsistent when one realizes that these "personhood" bills are intended to impact end-of-life issues as well. Most bills include phrases that approximately say "all people have the right to defend their life and liberties ... regardless of ... condition of dependency". This is intended to directly counter the pro-choice argument that suggests an embryo may not count as life if it can't live independently of the womb, and simultaneously cover the Terri Schiavos of the world. (TODO: re-find that citation that confirms intent... it was covered in a FAQ of one of the pro-embyronic-personhood organizations)

  So, if conservatives want to require hospitals to do everything possible to keep the Terri Schiavos alive, and the same law aspires to cover both birth and death, then shouldn't hospitals also be required to do everything possible to keep naturally unimplanted zygotes alive?

• In vitro fertilization may have restrictions put on it. Current practice is to fertilize a number of eggs, select the best ones, and dispose of the remaining ones. Disposing embryos would become illegal.
  59% of U.S. IVF clinics indicate they could do IVF without creating extra embryos
• All other forms of embryo screening would be outlawed.
• Fertility clinics often have large stores of frozen embryos (in case original fertility attempts fail). When the law goes into effect, fertility clinics would be required to find a human to implant each one in, they could no longer rely on being able to discard them.
  Fertility clinics could choose to dump most of their stored frozen embryos on the day before the law goes into effect. (albeit after consultation with each client)
• Embryo transfer would be treated as adoption rather than (as it currently is) as property transfer. For one, there would be a strict prohibition on exchanging money between the couples at any point in the process, to avoid any resemblance to child trafficking. (it sounds like embryos are already literally donated, but even if there's currently a "gray line" in place that discourages money from changing hands, it would become a bright bold line)

Other side effects

• If an illegal alien conceives of a child on U.S. soil, then the child could become a U.S. citizen on conception, not birth. (which might encourage foreign couples to start having sex as soon as they cross the border)
  No. It's U.S. Federal law that covers this, and 8 U.S.C. §1401 explicitly says that citizenship is gained upon birth, not "upon personhood" or something like that. Though there will doubtless be lawsuits over whether the intent of the federal law is to somehow allow the word "birth" to really mean "upon personhood"". Yeah, good luck with that...)
• Some/all miscarriages would have to be investigated as child neglect/child abuse.
  Unlikely. Government agencies already have to deal with competing demands after birth of "sometimes parents do malicious things and try to make it appear as if the death were natural" and "there really are quite a few natural deaths due to all the complications of childbirth". Sure, it's a small change to apply the same suspicions to unborn children, but it's not very different from what they already do.
• financial/accounting issues
  • Could they be counted as dependents for tax exemption purposes?
  • If a grandparent dies shortly before childbirth, would the unborn embryo get some of the inheritance? (e.g. if the deceased didn't leave a will, allowing the state to decide how to split up the money)
  • Could they be counted as dependents for food-stamp purposes?
  • Does the state have to give inner-city mothers a bigger welfare check as soon as they have a fertilized egg?
  • Can pregnant mothers drive in the HOV lane?
• other issues
  • when a census is taken, would unborn have to be included in the count?
    HR 1572, as introduced states that they don't have to be included in state or local censuses.
  • Could pregnant mothers be prevented from watching an NC-17 movie in a movie theater?
  • Could pregnant mothers be prevented from entering a bar because they would unavoidably bring along their minor?

Far-fetched side effects

• pregnant women could be forced to buy two theater tickets, or two airline tickets, since they legally count as two people
  It's extremely unlikely that corporations would choose to do this, because of the inevitable PR backlash. However, it's likely that a small company (that wasn't in full possession of its faculties) would do this sooner or later, which would trigger a court case, and judges would have to sort out the mess.
• images of fetuses would be considered child porn
  A photo of a nude child is not (usually) sufficient to be declared child porn, usually there has to be at least minimal sexual intent able to be read into it.

  Also, HR 1572, as introduced amends the ND law "Possession of certain materials prohibited" to state that it's only child-porn if "the minor is a born alive child".

More "minor" clarifications to laws

• The law doesn't currently recognize the ability of individuals to split or join, but all of this can happen inside the uterus. If North Dakota took the step of giving unborn babies state ID numbers, then there would technically need to be a process for splitting/merging them
  most splitting occurs within 15 days of conception, which is only a few days after hCG pregnancy tests are able to detect the embryo, and two weeks before ultrasound is effective, so it's likely to remain a theoretical exercise rather than practical problem?

References

• Ethicists ponder embryo personhood, Chicago Tribune, 3 Dec 2007
• Should Fertilized Eggs Have Rights?, Time Magazine, 21 Nov 2007
• Responses to Common Objections, personhood.net (decidedly conservative, see below)
• Abortion, Bioethics and Personhood: A Philosophical Reflection, Center for Bioethics and Human Dignity

• [Nov 4, 2008] Colorado's Amendment 48, a ballot initiative — failed with only 26.7% voter support
• [Jan 14, 1988] Reagan's Presidential Proclamation. It didn't have any force of law on its own. "This sacred legacy, and the well-being and the future of our country, demand that protection of the innocents must be guaranteed and that the personhood of the unborn be declared and defended throughout our land."
• Bills that failed to clear committee: (this is an incomplete list)
  • [Feb 10, 2005] Sanctity of Life Act
  • [Apr 5, 1979] Paramount Human Life Amendment
  • [Sep 12, 1973] Burke Human Life Amendment (rather than saying "at conception", it covers "unborn offspring at every stage of their biological development". Is that even broader? Or does 'offspring' mean that the pre-fertilization stage doesn't count?)
  • [Jan 30, 1973] Hogan Human Life Amendment

• NRLC (National Right to Life Committee) — has been against personhood for a while, for several reasons. NRLC agrees with personhood in principle, but recommends against pursuing this specific route. Some have said that NRLC believes personhood bills are destined to be struck down, or that NRLC believes it's more politically pragmatic to push for bills that allow for rape/incest exceptions.
• personhood.net — a website of Georgia Right To Life