“Blended families” may not be a legal term, and “assisted reproductive technology” (ART) may not have yet transformed the legal definition of parenthood. However, both are increasingly common in today’s world, raising some unique estate planning challenges for advisors.

It is common for estate planners and trustees to work with clients who are on a second or even third marriage. These unions often include children from previous marriages, happy or unhappy ex-spouses, and multiple sets of grandparents. The children may be minors or adults, biological or adopted. In addition, same-sex and different-sex unmarried partners frequently live in long-term relationships, often with biological children and stepchildren who in many cases are not adopted legally. These “blended families”—often referred to in the past as “non-traditional families”—require special care and consideration during estate planning. They may also require a close examination of the clients’ priorities and of the words “fair,” “equal,” “children” and “descendants.”

To complicate the situation, assisted reproductive technology has advanced so dramatically in recent years that there are new ways to add to a family. Many of us are now familiar with two common forms of the technology: artificial insemination (sperm injected into the cervix or uterus) and in vitro fertilization (IVF), a process involving the surgical removal of eggs from a female and then their combination with sperm in a laboratory. Following IVF, the fertilized embryos can be used at that time or frozen for future cycles by the donor or another individual.

In 1978, Louise Brown was the world’s first “test-tube baby”⎯conceived through IVF.

Since then, more than 4 million babies worldwide have been born using this method. In 2015, according to the Centers for Disease Control and Prevention (CDC), there were 231,936 assisted reproductive technology cycles (which go from drug stimulation through embryo creation) performed at 464 reporting clinics in the U.S., resulting in 72,913 live-born infants and 45,779 eggs or embryos that were frozen for future ART cycles. Although the use of the technology is still relatively rare given the potential demand, its use has doubled over the past decade. Today, approximately 1.6% of all infants born in the United States every year are conceived with such technology.

Almost 40 years after Louise Brown’s birth, society is still examining the technology’s legal, moral and ethical issues.

Consider the following scenario (based on real life): A couple meets with their new estate advisor to update their plan. Each of the couple’s three children was conceived in a different way. One child was born to a surrogate using a frozen embryo created with the husband’s sperm and the surrogate’s egg. The second child was adopted by the couple, and the third child was born using an immediate relative as the gestational carrier of an embryo created through an anonymous egg donor and the husband’s sperm. The existing planning documents, including several irrevocable trusts, contain a more conventional definition of children and descendants, which assumed a biological⎯“by blood”⎯connection between the parent and child. Such language was often written into estate plans as boilerplate to ensure that inheritances did not pass to illegitimate children. In this case, the language may have unintended consequences. Technically, none of the children was completely connected to both the husband and wife by blood, and this fact could potentially be used by future generations to thwart the couple’s estate planning goals.

The challenge in this case was to figure out how to modify the definitions not only to match the current specific family structure, but also to contemplate future scientific advancements that may become available to their children and more remote descendants. How could the couple provide clarity in their documents and guidance to their fiduciaries to ensure their estate plan matched their wishes?

Relying on state inheritance law is not a viable option for issues involving assisted reproductive technology. While the laws on adoption are generally well-developed and there is more guidance now on same-sex marriage following the 2015 Supreme Court case Obergefell v. Hodges, the law on ART has not kept pace with advances in technology. State laws vary widely in both the validity of gestational carrier and surrogacy agreements and in determining whether a child born after a person has died qualifies as a child or descendant of a trust or estate.

The applicable law may not always be that of the state where the client resides currently, but could be the law in the states where the client and his or her children and grandchildren could eventually reside or in the state specified in a trust agreement or determined by a trustee.

If the documents are not clear, the trustee must interpret the provisions in accordance with the grantor’s intent, which may or may not be known. In fact, there may have been no way to actually envision the circumstances at the time the document was created. If the trustee cannot make a determination about whether a child qualifies as a descendant, the trustee may need to seek clarity from a court of law, which can be an expensive and time-consuming process, not to mention the fact that the law in the state in question may not yet be determined on these issues.

If an individual or couple plan to establish a long-term, multigenerational trust for the benefit of descendants, the issues are magnified. They need to think carefully about who may be considered a descendant under that trust. Will a child born as a result of a blood descendant donating genetic material for use by somebody outside of the family potentially qualify as a beneficiary of the trust? Conversely, if a child is born from donated sperm and eggs with no genetic link to the family, will this child be an eligible beneficiary? What about the succession rights of children who were born from the genetic material of a person’s ex-spouse or deceased spouse, possibly without the knowledge or permission of that person, or sometimes long after he or she has died? (The oldest frozen sperm sample used for a live birth had been frozen 21 years.) Or what if clients are dealing with genetic material extracted from a deceased person who had not authorized it (“life after death”)? A new process that was recently in the news is called “in vitro gametogenesis,” in which adult skin cells can be reprogrammed to behave as embryonic stem cells, capable of creating embryos for implantation. If the clients are not sure of the answers to these types of questions, they should consider drafting the irrevocable trust as flexibly as possible to allow the trustees or a third party, such as a trust protector, to modify the trust if necessary.

However uncomfortable the conversation may be, professional advisors should not be afraid to raise these issues and guide clients in their thinking. If the clients are in a blended family situation, regardless of the involvement of ART, the attorney should make sure to clarify the dispositions and definitions in any documents. Clients should be encouraged to review their plans every few years to make sure the documents continue to operate as they intend, taking into account their current financial assets, evolving family circumstances and current law. Typically, the biggest issues to consider revolve around control over assets, fairness and unintended consequences.

If irrevocable trusts have already been established, there may be options under the terms of the document or state law to modify the trusts in a way that better defines the eligible class of beneficiaries. Grantors and beneficiaries can consider whether their states allow for non-judicial modification of a trust, or a trustee could consider decanting the trust to a new trust or changing the situs of the trust (its location), if permissible under the terms of the document, to make the documents better reflect the grantor’s intent. Does the trustee need to reserve funds for potential children for some period of time? If the documents are left unclear, it will be the trustees facing the greatest challenge when they are called upon to interpret the provisions of the trust, determine the class of potential beneficiaries and implement the trust terms.

It is important to not overlook other types of planning documents a client may have signed years ago—beneficiary forms for an IRA, 401(k) account or a life insurance policy or a contract relating to some form of reproductive technology, such as IVF. Beneficiary forms and contracts generally supersede the terms of a will or revocable trust. If these documents leave assets to descendants or to trusts for the descendants’ benefit, do the definitions of family match those in the will or revocable trust? Does the IVF contract have restrictions on the use of frozen eggs and embryos, including whether they can be transferred to other third parties, how long they should be preserved or whether they can be used following the death of the individual for whose benefit the procedure was performed?

Planning for incapacity is also critical, especially if the spouses have children from another marriage or when there are medical or legal decisions to make, including how to handle stored genetic material. There may be a conflict between the wishes of the spouse and those of the children. A durable power of attorney can be drafted to include language authorizing a spouse, for example, to decide whether to destroy or preserve the genetic material and to make gifts to a broader class of individuals than descendants. In a blended family, each spouse may decide to appoint a family member other than his or her spouse to make these decisions, or, in states that permit it, co-agents may be appointed. It may also be possible to delegate certain decisions to one person and other decisions to someone else, under the durable power of attorney or by separate contract.

Estate planners must grapple with the reality that each family is unique and there is no perfect, one-size-fits-all plan. However, there are many informed decisions and tactics that can result in a plan that reflects the scientific advances of ART and the potential for changing family dynamics so that ultimately the work of a fiduciary will become clearer and far less challenging.

Judith A. Saxe is a managing director at CIBC Atlantic Trust Private Wealth Management, where she is director of research and education for the wealth strategies group.